I've been called everything from hot, sexy to gorgeous and receive looks every time I go out. When I was younger girls would whistle and yell and so on (for qualification to your question; sorry I can't post a pic due to school and an upcoming career).
You can tell who is only into you for sex when all they focus on is sexual topics and your body. They'll generally be the ones to bring up the topic of sex early on and talk about what they want to do with you. The focus will be on your looks, in relation to everything. Like being around a Paris Hilton who says "you're hot" all the time. They won't mention anything about your personality or anything else. Most of the time they won't want a relationship or even think along those lines. They might even be surprised that YOU want one, based on the assumption that you probably get a lot of action and so on. They will generally want an FWB type situation and the bolder ones will even say that's what they want. They usually aren't the loyal types (if any of them really are, lol).
Understand that all girls will like you because of your looks, and some might even be in denial about what they really want -- even to themselves. So at first it will be hard to decipher who's who. Most of them will probably have a crush and think you're the best thing ever, everything you do is perfect, head above the clouds and all that. But the ones who genuinely like you will say things like you're sweet, or a good catch, on top of you're attractive (and no, these aren't the kiss of death as it's commonly claimed). They'll also try to get to know you on a personal level better and focus more on the relationship route. Things that you can do together that you mentioned that you like in passing (which you might have thought of as no big deal; they hang onto every word). This isn't the same as being in the friend zone, so don't get all worried and assume they just want to be friends. Most girls won't hang around you or ask you questions and act all excited or (especially) touch you, give you compliments, remember everything you say, etc if they just want to be friends. The signs of disinterest will be clear when they just want to be friends. I never had a girl who just wanted to be friends who even acted like a real friend -- more like a way of them to feel superior by rejecting. They weren't kind, didn't give a damn about my interests, asked no questions, didn't want to hang out, acted like ****s, etc. Guys who aren't attractive generally don't have girls hanging around them and acting nice and doing favors. They're not acting this way because you're "nice" -- it's because you're hot in their eyes.
For those wondering why he wants someone who cares: it's probably because that's a greater challenge. When something comes so easy (like interest or sex), it's not as valued. But I've generally found that girls don't like you for you no matter if you're in high demand or not. They only like you because you're hot, or have social status, or money, or the usual. You can tell because once the infatuation and new exciting wears off, it's business as usual. Once you're on the other side you can see why hot girls act the way they do, because a lot of it is similar.
. And ‘you’re very charming’ recently, by a lesbian.