TL;DR you no read, you no receive. simple as that :D
So, I'm just going to rip off of elix's ideas here. I have created a private giveaway for portal bundle. This probably going to be my last giveaway for a while. (I've said that phrase for at least 3 times now, I'm not sure if I'm ever going to stop making giveaways) Anyways, let the rules and limitation commence.

Rule Number 1:

Anyone can enter as long as their only wins have been either a developer's or one of which they did not receive the game from. But, if I go on to look at the creator of that giveaway and he has only 1 not received out of a lot, something will be fishy there, very fishy.

Rule Number 2:

You must not own either portal or portal 2 as I don't want one copy to go into oblivion. (This has nothing to do with this paragraph, but (Vann Buzz zoo Kill xehanort)) As I don't want my good but twisted (oh so very, very twisted) will to go to waste, don't enter it even if you get a copy of the game. Actually never mind, you could enter it if you either have 1 or 2. I'll just hate you most likely for the rest of my life. :D

Rule Number 3:

You must not have broken SG rules or have reformed with some proof. As I know that in parts of the US some time ago, you could not drink unless you had the "intent" of eating. As you can imagine many had the intent to eat but didn't. So, I won't just believe in words. (in case you didn't get it, the first letters to the words in the parenthesis inside the parenthesis in rule 2 is the code you need)

Rule Number 4:

Once you are in the giveaway, you must read the rules once again. Failure to comply means I will reroll even if you win. But, how will I know you read the rules in the giveaways too. Trust me, I'll know. I always know. Where you are. What you ate. Who you are. When you go to sleep. But rest assure, I won't post any of your information even if you tell me too. :)
PS. I think some people don't know this yet but for each giveaway, there is a 5 character code for it so that you could differentiate between giveaways of the same game. So plug in the five character code after steamgifts.com/giveaway/