Giveaway noob

1. Whatever you want. I usually put mine to a week. I tend to have a 3 days minimum

2. That's correct. If a game was free at some point it can't be given away here.

3. You could ask the winner if they're okay with a deletion of the GA. Most will be, but if they're not, you can only either buy them the game or accept that you will have a not received on your profile.

1) As long as you want. Week sounds fine to me.
2) Correct.
3) You have three possibilities: either give the winner a working key, live with the 'not received' feedback, or ask for the giveaway to be deleted; you need the winner of the giveaway to agree in the last case.

can I send a different game if the winner agrees on it?

No, this is against the rules.

1. One day is enough
2. Yes, that's the meaning behind free games
3. You have to give the winner an other key for the same game

1) Depends on how many entries you want. And the parameters used. For public lvl0, 1 hour is more than enough to get hundreds of entries.
2) There's an unofficial list somewhere in the forum of games you can't give away through the SG system: here (those games you can give individually to other users if you'd like).
3) The winner would have to agree to cancel it. There was a similar thread a week ago. Here

Note that you have limited giveaway slots so making 1 week giveaways for 4000 games in going to take a while.
If you haven't yet you should take a look at the FAQ.

1)If u wants to send alot of giveaway quickly u can ask for slots from support team or just create a giveaway that last only 1 hour :D
2)Yes
3)You can provide another key or just ask whether if the other person accept to delete the giveaway

1) What is a sensible amount of time to run a giveaway? I set my two as a week, but now I am thinking future ones should be shorter...?

Two weeks is a long giveaway. For public ones, time does not really matter. You'll get entries, as long as it's not DLC for some obscure game nobody owns, and/or you've set it to level 10 (and it's a game a lot of people already own, or don't want), even if it's just a 1h giveaway.
For forum giveaways, most giveaways will get enough entries for CV quite fast. But if you want to make sure that more people notice, a day or two is a good length. But it's up to you.
For group/whitelist giveaways, it depends on the size of the group/WL and the game. Between 1 day and 1 week should be good.
But in the end, it's up to you and how you want to do it. If you want a lot of people to notice the giveaways, then longer is better.

2) The guidelines say that you cannot giveaway 'free' games. Does that mean games that have been given away free in the past, even if they have a price on Steam now? For example games like Crystals of Time, Make it Indie, Deadbits?

Correct. A game that's given out for free gets removed from the giveaway list, so don't worry about older ones.

3) As some of my Steam keys are very old - from Indie Royale days, as I have been adding keys on to my own Steam account I found that some keys were 'duplicates' - not many, but some definitely weren't accepted. None of my keys have come from illegitimate sources, but I suspect some keys may have been revoked after bundle sites closed down, or otherwise. If I give a key away and it is a duplicate, how do I deal with that? In some instances I have several keys for a title so will be able to send a replacement, but some I do not - in these cases can I send a different game if the winner agrees on it?

No, you have to give away the game that you're making the giveaway for. If a key ends up not working, then you need to get a new key from somewhere else, or ask the winner if it's okay to delete the giveaway. If the vast majority of the keys work, it might be worth doing some group and/or Whitelist giveaways with people you know are fine with deleting the giveaway. Just keep in mind that every time you delete a giveaway, you permanently lose a giveaway slot. You'll get a new giveaway slot for giving away 3 games successfully (it does not matter how valuable they are, as long as the giveaways were marked as received, you'll get the new slots).

What is a sensible amount of time to run a giveaway? I set my two as a week, but now I am thinking future ones should be shorter...?

Always ask yourself if you like GAs like that and then decide. The chance to win a public GA which lasts a week and it's for lvl 0 is almost zero (often less than 0.01). I doubt anybody like GAs like that. If you want to please also GA creators and not only leechers with lvl 0, make your GAs with less entries at the end.

I would never make a public GA longer than few hours. Just group, private or whitelist GAs should be longer. A week is enough for them.

1) Whatever you feel appropriate. The amount of entries is more dependent on level setting than anything else - I assume most people enter GA-s from the first few pages only (bots can be more "patient" and reach the last pages). 1-2 days are a good pick. Longer has little effect, shorter causes people from different time zones to be left out (as they are sleeping for example)

2) Free games are removed from the list after some time - the clause mainly aims the temporary period when XY site gives away something for free, but it is still available on the "Create giveaway" list. If something was given away for free on Steam (like Payday and some other games I can not recall), giving them away is okay, since people either have those games, and can not enter giveaways, or they have not activated the games on that given day/days, and they can not do so any more

3) If a key does not work, you can replace it with another one. You can also delete giveaways, just then a GA slot is gone (you start with 3 at the beginning, and the number of them gradually grow as you send gifts - one new slot per 3 successfully completed GA-s). Different game is a no go: winners have to activate the game they mark as won in their profile. Otherwise it is a non-activation which leads to suspension (see table on the bottom of "Roles" page, linked in the footer of all pages - https://www.steamgifts.com/roles ), and is basis for reroll requests too

Pro-tip:

If a winner receives a non-working key, you could give them a key for a game that was offered for free as a bribe to get them to agree to letting you delete the giveaway (if the actual key doesn't work)

1) What is a sensible amount of time to run a giveaway? I set my two as a week, but now I am thinking future ones should be shorter...?

Giveaway duration is purely a matter of personal preference, except in circumstances where you're trying to balance the end date around your real life schedule, or make sure the giveaway ends before (or after) the sale with the game in question ends, or so forth. There's no real benefit to a particular duration inherently, though many users favor short-duration giveaways for the lower entry count (and thus, higher odds).

2) The guidelines say that you cannot giveaway 'free' games. Does that mean games that have been given away free in the past, even if they have a price on Steam now? For example games like Crystals of Time, Make it Indie, Deadbits?

Any game that had a tradeable copy (ie, steam key) given away in a large-scale promotion before. Games that were free on Steam itself (and thus not tradeable) aren't an issue. Really, don't sweat this one- other than games in current promotions that haven't gotten attended to yet, any game that would qualify for this has been removed from the giveaway creation list, so you won't be able to create a giveaway for it anyway.

3) As some of my Steam keys are very old - from Indie Royale days, as I have been adding keys on to my own Steam account I found that some keys were 'duplicates' - not many, but some definitely weren't accepted. None of my keys have come from illegitimate sources, but I suspect some keys may have been revoked after bundle sites closed down, or otherwise.

GreenManGaming and IndieRoyale keys are notable for "expiring", the first due to GMG policy, the latter due to IndieRoyale being.. well, dead and poorly managed before that. IndieGala keys have a much higher than average rate of having problems in purchase, and you wouldn't be able to make a case for replacement after a long duration if that were the case [assuming you could even manage that out of IG's terrible support, anyway], so it's effectively similar. HumbleBundle and Groupees and BundleStars are all very reliable sites, but even they seem to have max durations for support [though in HB's case, they've still helped me a year after the fact].

Your best bet for keys you're dubious about is to create a group for the giveaway and make sure everyone you invite to it is fully willing to "agree to cancel" if the key turns out to be faulty. You'll lose a giveaway slot when the giveaway is deleted (you start with 3, and gain one additional slot per 3 completed giveaways), but that's easy to regain. Other than that, if they agree to cancel, you're in the clear.
Public giveaways or giveaways for open groups tend to turn out very poorly for getting agree-to-cancels.

But, that all aside, with the sole exception of GMG keys, the odds of a key being faulty are very, very low, even for the other 'problem' sites.

If I give a key away and it is a duplicate, how do I deal with that? In some instances I have several keys for a title so will be able to send a replacement, but some I do not - in these cases can I send a different game if the winner agrees on it?

If you can't replace the key, and you don't have a respectful winner, you'll end up with a Not Received mark in your profile. That's not inherently an issue, but too many of those and staff'll take note. Some users will also blacklist you if they see too many of those, and most users will tend to be more dubious toward your trustworthyness if you have too many of them.

You must always provide the exact game listed.
You can offer them another key if you wish, as an apologetic gesture, but the giveaway itself still has to be deleted, it can't be replaced with another game.

1) Give enough time for at least 5 entries. That means a level 7+ will need a week, while a 1+ GA needs about a minute (over is fine, it's up to you).
2) Freebie games will not show up in the list when you create a new GA.
3) https://store.steampowered.com/account/licenses/ might help you match up activations with bundle purchases. Also Keys Added. I've found very old keys still working, but if you think you've gifted one away, make it a free "bonus" for one of your GAs or something (getting no CV), or prepare to buy a cheap working key from some steam trader.

Thanks all, you've all sorted this out for me :) In future I'll be running giveaways for a max of 3 days, and the potential for any non-working keys is miniscule anyway so I will deal with itas you've all suggested if it does ever happens :) Thanks!

as for number 3:
a user once stated that you must agree to his rules in advance, and then he will invite to a group and make the GA for that group.
i.e. you can make a group that says if any key is dupe they agree in advance to allow a deletion of the GA.

support approved of that. but i wouldn't make it into a habbit ;)