Well first off. When you trade with a person and they put an item in or they ready for the trade it will say in a yellow box (Somewhere on the top of the trade box thing) That they don't have the authenticator or if it hasn't been online for 7 days (The authenticator not the account).If you want to get games though you shouldn't really get them like this as it's a pretty dangerous way of doing it. (Or atleast that's what i heard.) Rather search up on google a website called G2A if you haven't heard of it before. They sell games for lower prices. (I'm not advertising!) There's my fifty cent

I disagree about these other websites selling games for low, their sources are often shady and if your games got revoked you have to deal with them to get your money back.

The outpost way is more safe if you follow some simple rules: always make the trade fully through the trading window, do not just send the keys and let the other side gift you the game. And compare the prices, use something like steamprices.com to check if it is possible to make profit by selling at that price if the game was bought in your favorite low price region, and if its not or way lower than everyone else selling at, stay away.

And if your game still got revoked, valve usually reverses the trade without a hassle.

And this 7 day lockout only happens after you accepted a trade and it went into escrow and you cancel it while its in there, it doesnt happen if you just cancel the trade.