For me, it's usually when they act like they like me so much even though we don't know each other really well. Because of course, what else do they have to go on but my looks? That turns me off quicker than anything else and I get rid of them.
Another way to tell would be to see if they pay attention to the things you tell them, if they remember little details and everything. Because that means they were really listening, not just looking at you. They also might only use physical things to compliment you, instead of your personality traits.
A guy text me yesterday '' you have a sweet face , bangin body , and beautiful a$#''. Very random, but all 2 common . I notice when guys are only interested in me for my looks when its all they talk about . It doesn't do much for me , but then I suppose its because I don't flatter easily . I don't test where anyone's head is truth of the matter is time will reveal personal intentions. If I have suspicions of someone being hung up on my looks I won't even bother , I mean what's the point ? There's more to me then the physical when people recognize that I respect them a bit more.
Well normally for girls, at least for me, the looks factor will only be a reason for so long. Within a very short period of time it has to be about personality or I get bored. However, see if you guys communicate alot. If she's interested in more than just hooking up or showing you off. If you feel like you connect on an emotional level and have good conversations then it's about more than that.
there's no way to tell for sure, but you should ask yourself. is he/she making you feel uncomfortable? do you guys talk a lot? does he/she seem genuinely interested in what you have to say? it's extremely hard to tell, but don't be afraid to trust your own judgment.