Je ne crois pas que c'est possible de savoir de l'extérieur. Il y a les indices, par exemple si je vois "new girls every day" je le trouve très méfiant. On peu demander des filles, mais elles ont des raisons de mentir.
I was always kind of uncomfortable with agencies, I understand they can be beneficial in some cases but they're also more likely to involve exploitative situations. I guess I'll stick with indies, this is just another reason.
The way I see it is if you're having sex with strangers regularly you have to assume you're going to be exposed at some point. The smart thing to do is manage your own risk by getting tested regularly. Someone can be recently tested and still give you chlamydia.
The only scenario where sharing...
I don't ask for tests. Like Luna said, it's highly private information, easy to fake and not that reliable in the first place. If you're super concerned either don't do it or take your own precautions with things like DoxyPEP.