Help

I haven't ever bought a game from g2a
i am kinda confused how the system works, it tell mt the game is "$X" then when i check it it would be wayyy cheaper
if anyone is experienced/ knows a better site for cheap games, please help me
Thanks!
P.S. the games i mainly want to buy are payday 2 and borderlands 2

I've bought games from g2a like Battlefield 4 so they can be trusted just buy off people who have 5 stars and if you don't trust em get the g2a shield