I'm just thinking - I was a session provider...the last thing I'd do, even if F/S was on the table, was to put that out via email as a written expectation. It would be a total 'vibe' thing, if I was feeling it, depending on chemistry - aside from putting yourself out there a bit too obviously from a legal perspective, it's just not something I'd want to agree to sight unseen, depending on the person. That was if I was open to the idea at all.
This is why "YMMV" as a saying exists.