Basically you should avoid any agency that asks for money from you. If you're good the agency will make money off you and you don't have to pay them anything.
Was spotted by a friend of a friend who worked in a talent agency. Went in and they took some photos and general details like height, etc. and then they put my photos forward for some jobs. Finally got one for a TV commercial which they paid me for. I didn't have to pay them a dime for any of it.
Depending on the work involved some agencies will try to fill their books with all different types of people as sometimes 'every man' or 'every woman' types are wanted for TV commercials. Just look at the TV adverts in HK and you'll see they're not all your stereotypical model types. For print ads and catwalks it's different.