I'd like to think im a nice guy, I try to be honest as much as possible and do wee good deeds here n there when I can (holding doors open, helping elderly or frail people with their bags etc) and I go to the gym, granted im not massively muscular or that good looking (quite an average looking guy if im honest!) but I'm also a massive geek currently in a IT job who loves star wars and star trek and playing video games lol.
So I dont think you can stereotype people like that, similarly I've met wonderful people in the gym who are more than happy to spot me on bench, give me advice on what works for them and so forth, yet for all I know they could be a womanizer behind closed doors, its not that easy to tell.
I think as long as you like a guy and find him interesting thats a good starting point, its up to you from then on if you want to form a deeper relationship, if a guy has honest intentions and truely likes you, he'l stick around and take things at whatever pace you want, those who just want a quick (excuse me for saying this) ride, will just get bored and move on if they dont get what they want before long.
I know thats a very black and white way of putting it but, I think most people should know themselves if someones worth being with, dont always go on looks alone, afterall looks only go so far once you get older, and no one wants to be with someone whos not a good match for them, or just a horrid person.
Hope this helps!