There are may places to get good prices on games.
Due diligence is suggested, as if you make a purchase from a shady seller, then it ultimately will be you whom is out of the money.
-Ebay can sometimes have good prices for steam keys, and Ebay, if you use Paypal, has some-what of a guarantee.
-Kinguin.net Kinguin.net is decent imo relative to g2a which is often not talked about favorably. On Kinguin, with some of the sellers at least, you have the option to pay a very small fee for a 30 day guarantee of your purchase. I paid 42cents on a $42 game. This came into account when the game I had purchased eventually was revoked. I contacted Kinguin, and within a few days I was refunded the cost of the game.
Nuuvem.br often has very prices for games. I've purchased over 30 titles from Nuuvem. With customer support they are quick, and very easy to deal with.
There are services that will help you to find lower prices and/or pricing history to gauge whether you're getting a deal or not.
Enhanced Steam is a nice browser plugin that I find very useful for locating quickly the lowest cost a game has sold for(in order to know around what price I should be able to expect to find), where it is cheapest at any given time (the sellers they list/use in their pricing are usually respectable outlets, that sell officia keys). It does not include sites like ebay, kinguin, or other re-selling types of outlets.
The best place I could mention for anyone to find good deals on games, at least for my time, is http://www.reddit.com/r/GameDeals/
All in all there are a ton of sites out there to find great deals. Buy at your own risk, and make sure you know what recourse you have if you are buying from non-official sites/outlets.
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