I think they're legal, but "sketchy" is a good word to use. I'll be honest, as a 23 year old guy, I find some of the late teen models for these sites being spammed to usenet are pretty cute. One in particular "Lalana Model" is damn fine, no idea if she's 18 or not, but she's hot. Sorry but it's in my genes!
There's a particular example of this type of site I remember, cause the asshole used to spam the living HELL out of usenet, including the nospam.teenfem group where spam is not permitted. It was molly-model.com (cutie!) which was run by Gary Smith. He also ran photostudio17.com which had multiple models. As I remember it turns out the guy had prior convictions for feeling up an underage girl in Arkansas and also got convicted of taking illicit pics.
NOTE: I do NOT have any proof of this, and I did a search but couldn't find much regarding charges aside from the ageofconsent.com link below, so take it with a grain of salt. This is not meant as slander/libel, but just what I remember at the time. There were several TV news website stories posted to usenet when all of this was new and interesting, but I can't find them at Google. It's possible that the guy's never touched a girl in his life so I'm not making any accusations.
For awhile there was somebody posting his mugshot from the sex offender registry into usenet.
Here are some relevant references I could find in a Google search for Gary Smith and "PhotoStudio17"
http://ynotnews.ynotmasters.com/issu...501/page6.html
http://www.avnonline.com/issues/2001...c1001_02.shtml
http://www.ageofconsent.com/comments/photogbusted.htm
http://www.glgarden.org/Dissident/Di...delVideos.html
I'd be interested in seeing other info about Gary Smith if anyone's got it.