like others have said the black sopt on the fin isnt a 100%. I personally have a !00% proven male with a pretty big blck spot on his top fin.
on the advice tip... IMHO if you find yourself discovering reasons to lean towards getting rid of the fish, then deep down you prolly want to go that route.
its been my exp that when you start noticing undesirable things about your fish its kinda like a way to cope with a decision you are conflicted with. i e letting your fish go. hope the advice helps