You could do that if it was trade for gift, and game was removed from your library/inventory, but you just gave him keys. Steam won't give them back to you, cause you shouldn't trade beside trade window.
EDIT: you should remove this negative rep from his profile since you didn't traded with him.
1 decade ago
Permalinksure, but only to get confirmed this is a scammer http://steamrep.com/search?q=http%3A%2F%2Fsteamcommunity.com%2Fid%2F_Comparison%2F
1 decade ago
Permalink1ly: report him via steam acc: http://steamcommunity.com/id/_Comparison/
2ry: report here: http://steamrep.com/search?q=76561198100441208
1 decade ago
PermalinkDisplaying 1 to 3
Closed 1 decade ago.
http://www.steamtrades.com/user/Comparison
http://steamcommunity.com/id/_Comparison/
STEAM ID: STEAM_0:0:70087740
What now?...
I have first sendet the Keys and then going offline -.-... Have not payed.