They may not necessarily be perverts although you need to be aware of the risk. However, many photo studios hook youngsters in with flattery, give you a photo session then start suggesting the charges involved eg so much if you want a copy of your photos, so much if you want your details given to modelling agencies, and a percentage if you get work from said agencies.
A good guideline is to check out the premises and address they give - are they a known and established firm? does it feel right? What other photo work do they do eg weddings, schools - or are they seedy and dodgy.
Lastly, always remember that if something seesm too good to be true it probably is not true, and that there is no such thing as a free lunch. I am sure you are a gorgeous individual, but given the effort, time and money put into their careers by professional models, is it likely on balance that you were picked out as special. If you feel confident that this was the case and that the firm are OK, then go for it.