Do guys lose respect for girls that have sex with them right away?

Not really in my eyes!

99% of the cases, no, they don't have respect because now they see you as a sexual object, and as an easy target.

I always have told my female friends, that for the most part, you will know if a guy really likes you, when he is not there just trying to get sex. Kind of a weird advice, but here is how it goes for me. When I really like a girl, and that mean, when I see her as a long term committed type of girlfriend, then the last thing I want her thinking is that I'm there for the sex, so I'm willing to wait for her to express that sex is ok. And because I like her that much, I'm willing to wait.
When I see a girl just as a sexual target, I try to have sex as fast as possible cause I don't care what she thinks about me.

Yes and no. It depends on the guy but in mos cases, yes they do because they figure if you were so easy to give it up so soon then you must have done that with other guys. I mean, don't feel bad if you do something like this once in a while but really always make them wait. Patience is good. Also, just because you have sex with a guy the first day yall meet doesn't mean that he will always lose respect for you. He may like you a lot then later it can become a relationship. Overall, most guys (Good Guys)rather have a girl who doesn't give in so easily. Bad guys like players ddon't really care either way they lose the respect once they get. So its not about how early or late you give it. Its all about who you give it up to. But for your own self respect and love, make them earn it.