No, unless you are around fenime stereotypical gay guys, you cannot tell who is gay or not other than asking them and them being honest about it. Most gay guys who aren't on the scene (but out of the closet) such as myself are straight acting. Also there are no music/movie preferences that can tell for sure that a guy is gay even if they listen to fucking 1D and most gay guys listen to the "straight" music, so that's a dead end too.
However if you have sex with guy, it's easy to tell if they are gay or not. Gay guys will be passionate and involved and it's easy to tell whenever somebody is genuinely enjoying to do it with you or they are in just for the money. Besides, unless if you are actually paying them a rate in hundreds of the dollars for the sex, you probably won't ever have this problem. Gay for pay tends to not be that dedicated and involved, nor willing to go in relationship with you to eventualy benefit for it. They are typical man prostitutes, they will only do it with you after you pay them. This is a huge blessing we gays have, that straight couples don't: Nearly no money sluts and the ones that are out there are obvious: They will charge you money to have sex with you.