At the risks of sounding harsh, money. Would be best if come without any obligation whatsoever. Just free money.
On a serious note tho, provider will need to bullshit (or at least be ready to fake it) so to give the illusion that they really enjoy the session. To give that sense of achievement to the client as if they managed to satisfy the provider's need.
Other note might worth considering, some acts might be too 'intimate'/ 'personal' which the provider reserves for non-paying hook-up. Something for his own real connection, things that are not for pay.
Alternatively, specifically hire providers that are looking to be serviced by clients.There are some out there.