Does it look infected or anything? Or like something the fish will be able to live with?
Call me crazy but....I love fish with a handicap,they're the best
,so what if it has a bit of an attitude, it must feel as though he has to show his toughness so that no one takes advantage of him because of his bad eye.And he'll probably venture around more once he realizes nothing's going to hurt him in that tank.
I had a compressiceps once with only one eye, she was like that when I bought her & it made me love her even more, she was awesome!! And she let no one push her around
She had a baby front who was really buddy buddy with her and the front would always help her find food because she'd just spin in a circle at feeding time
If you take him back he may not ever get a home because of his eye,people may say "uhhm,not that one" about him at the lfs and he'll live a terrible pet shop life
, let him stake out a little piece of the world to call his own in your tank
What kind of fish is it?