can i trust this site

For Gaben's sakes....

Why not use the search function? This question has been asked (and answered) several times ¬_¬

http://www.steamgifts.com/discussions/search?q=g2a

i've bought 4 games from there without any problem, though it's user based and it's possible to experience bad situations.

G2A is now a pure scam. Steam now censorns it,and Youtubers/Twitch streamers who advertise this site must feel bad. Because it uses third party reselling(users of course)and why its hated because the resellers usually sell stolen/broken keys and thus must be avoided.

I didn't had trouble at g2a, but the problem is that their key are not always legal (cf : the far cry 4 shit that happened not a long time ago)
This kind of site are just buyings loads of key really cheap when they can (like in humble bundle, even though it should be one per person)

If you wanted to know if you will receive the game you paid for : Most probably yes.
If you wanted to know if this site is legit and morally correct : i would say no.

it looks like a ref link. he wants to milk you.

As far as I know it's safe to buy from there. As for the guy wanting you to buy from there he most likely has games for sale there and he sents you to his link so he make more profit (link you posted expanded :https://www.g2a.com/diablo-3referalllinkthatwaspostedl)

Problem with sites like this is advertisment, youtubers (looks angry at Pewdipie and LevelCap) use the site to make money, the fans buy the game via their ref link that they spam everyday (cough LevelCap cough), thos making the site apear to be legit, what on most part it is, but its not an authorised re-seller, making the keys/gifts you buy easy to revoke. My opinion is stay the heck away from it, you are even better off in the trading section.

I bought some keys from there and it worked fine. If you buy game from g2a using that link, he will receive some $$$. That is g2a goldmine reflink btw.