You'd be surprised that this isn't always the case. Reputable agencies can also be fooled by fake i.d. and there are underaged girls who easily look considerably older in some cases. Nothing also prevents an advertising indy from also claiming she's 18 or 19. I've also seen an indy or two advertising their age as being 18 or 19 when they had been working for a well-known agency or so for a couple of years previously. Years ago an sp i met when she was 21 confessed to me during conversation that she started to work as an sp when she was underaged and that her 'boss' was aware of it from the start. Another admitted the same thing but added that her 'boss' only found out months later but by then she had turned 18 and that's why she had spilled the beans to her 'boss' and that's why she wasn't fired. I've heard all kinds of stories over the years which only goes to show that nothing is 100% proof.If someone books an agency escort, or independent affiliated with merb, they can be sure she is an adult.
But yes, in most cases well-known reputable agencies are more careful about whom they hire and often will routinely screen better than others prior to hiring someone, but the odd time someone likely does manage to slip through the cracks and it's never wrong for any suspecting john to be vigilant if he has any doubts at all when meeting someone.