G2A grey market reselling bussiness and their resellers

I guess more revocations coming and faster in future:

With today's server update, it should now be possible for Steamworks partners to revoke your own CD keys. If your Steam account has CD key management rights, you should have a menu item to Ban keys, under the Tools dropdown.

At this time, revoking keys should only be done for fraud cases. Customers are shown a specific message when their CD key has been revoked. Also you can only revoke a maximum of 200 keys per batch. This limit is mostly to prevent possible load issues, as we need to check that each key is valid and associated with the account that is trying to revoke them.

And finally, be smart about revoking CD keys. We cannot undo any bad revokes that may happen, so only ban keys that you are absolutely sure should be banned.

I prefer kinguin, cekeys and instant-gaming. Don't see what's wrong with buying from them. Yes you can get scammed, but most of the keys and gifts are legit. Anyway the price there are not so great, legit sellers often offer better deals.

I buy re selled keys often, so i will make a huge post with all i consider relevant.
Im not sure about Kenguin, cause i never used it, so i will focus on G2A. I bought there a lot, and i never had any trouble. I also sold 2 keys there just to see how it works. In my experience:
For selling keys, what i noticed is that they keep a big percent, and as a safety measure, you cant use the credit you earn untill 15 days after you get it (as a safety measure to undo the trade in case you scammed someone). Im 100% sure my keys worked, and yet i didnt get a positive rate as a seller (nor a negative), so i guess its common for people to just forget to rate.
For buying keys, you can pay an extra euro for an insurance. As soon as your payment is deposited, you get a mail with the key, so you can open steam and use it. If it says duplicate or not valid in any way, you log on live support and tell them, they will guide you. That only happened once to a friend, in a very shady purchase (AAA title worth arround 70usd, he got it for 15usd), he didnt have the insurance, and he still got his credit back. After you activate, you have (i think) 15 days to rate the seller (you should probably rate him when that period is about to end). There´s no risk of getting a random code made up by the seller, because you would be cancelling the purchase, getting your money back, and he will lose the profit while having to pay the taxes anyway, and also he will get a bad rep. In that situation, most sellers prefer to give you another key instead of getting the trade reported as a scamm. There is however a risk, and that risk involves key revokes. The dev is entitled by steam to revoke a key anytime he wants, for any reason. This opens the window for you to buy a key, activate it with no problem, and maybe 3 months later you get it revoked. Some keys might have been purchased using stolen cards, and some devs might pass the lose to the final buyer of the key by revoking, even after some months ( and after such a long period, im guessing you cant get your cash back). In this sense, its risky, but only as risky as trading gifts on steam.
Also, there´s something to be said about the ethics. Re selling keys might be considered damaging to the devs. When a bundle comes out, you might get a game for a real small amount of money, so it is common to see that many people buy the bundles at low cost to resell the key later. When this happens, right after a game is bundled, you will see that game at G2A selling even for cents, sometimes for weeks, sometimes its months, sometimes those games stay at those ridiculous low prices for good. When that happens, many potential buyers of the game (those not scared to buy from G2A) will buy it from that website because of its low price, so the devs will lower their sales untill the price at G2A goes up (untill all those copies are sold). I use G2A because i believe games, as any other thing you pay for, should be allowed to be reselled when its posible. There is no law against it, and im from a time when games were physical copies, people bought them, sold them and rented them, and everything was fine. Also, in this particular case, you have to notice that the devs already got paid for those games selling cheap at G2A, because most of those copies were sold legally, and they got either the price they were asking for, or the cut they agreed with the sites that sold the keys (like HB, BS or IG). When people complain about G2A, i think this is the one thing you have to really consider. Its pretty much a safe site, but it is true that when devs make such a terrible choice as to make a massive giveaway or bundle a game that not many people wants to purchase, a site that makes re selling so easy makes the devs pay more for their mistake (same as if you sell shoes and you decide to give away 100k shoes, and then you realize nobody is using them, but trying to sell them at ebay for 1usd). In this sense, if you feel like suporting a dev, you might want to spend a few extra cash and buy from their website.
Finally, i did tell you there was a chance to buy a key and get it revoked even after months. Usually, when you get the key its already revoked and you cancel the purchase, but just in case, you should always check the user reputation (and the amount of sales), and most important, have common sense. If you see a game that never had been on a giveaway or a bundle selling for just a small % of its price, be suspicious. As an example, Dont starve togheter right now is selling for arround 8 euro and its just 1 copy of the 2 you get when you buy the game on steam (if you do the math, that game is actually more expensive on G2A), so if tomorrow i see it for 4 euro, i wont buy it untill i find info on why its price lowered. Valve games are usually way more expensive than at steam because they avoid re selling by making the copies you buy during sales untradeable. When it comes to preordering AAA titles, they will be cheaper on G2A, but not that much. Notice there is no safe way to be 100% sure your key wont be revoked, just an advice to have common sense.
In my experience, i never bought a game (specially an expensive AAA game) too cheap compared to its price on steam, unless i knew there was a big sale, bundle or giveaway before. I did buy AAA titles when they came out as preorder (for instance MKX), but it had only a small discount compared to steam (like 25% off). Also I usually pay for the insurance only when the price of the game is over 3 euro (wont spend 1 euro on a game that i am paying 30 cents). The main use i give to that website is buying games at the same time they are beeing sold bundled at HB, BS, etc. or if i cant grab them from a giveaway (G2A has a payment option that´s way better for me, even if i spend more cash). With this behaviour, i never had problems, and ive only heard of a few from the people i know. When that happened, their live support solved it fast (even without paying insurance). Also, i have games i bought there for over a year, and never got a single key revoked. I believe its as safe as you can get for a re selled keys market, and lately they did a lot to make it more transparent in response to devs concerns.

I am going to pipe in here.

There are some really strongly opinionated and worded posts here arguing over a lot of nothing.

My opinion is this. I have never had a problem games/keys/gifts purchased from Steam, Humble, IG, or Bundlestars. Nor have I ever heard of any legit complaints from them.

I have had problems with G2A. The fact that so many have to dig so deep to make this site seem legit tells me its not. You don't need 1000 word posts to prove a site is legit.

Never had any uses with sites like g2a bought over 20 triple A games there for more then 50% off never got a key that didn't work or has been deleted from my steam later on and i have been using these sites for over 2 years

And a game like fallout 4 is 20$ there and 60$ on steam its worth the risk anyway can buy 3 keys for that if 1 is fake thats still worth it