I think it would be best to not date them, because, while you see it as giving it a tentative sort of opportunity and see if it actually leads to something, they're thinking "I just need to work this a bit more and then scooooore!" (whether "score" means sex or just a more serious relationship or both depends on the guy, of course).

They're seeing it as a small victory paving the way to bigger ones, instead of a trial run.

If they're pestering you and needling you over and over even when you say no, they're not likely to listen or be very perceptive to anything other than you being firm about your decision and sticking by it until they give up when they see you're serious.

...The bad side of this is that some might take it personally and blame you for it not working out by not even giving them the chance, but it's up to them to keep looking for someone actually interested, and it's not really your problem that they don't accept your agency as a person, at least beyond making your boundaries firm and clear.

On the good side, you owe it to yourself to settle only for someone you really want to, instead of giving in to doubts and pressure (even if it's only the pressure of "geez, okay, I'll do it, just shut up already", which can be more draining than you'd imagine.)