I kept my boat at TMM for many years and sold time on many occasions, mostly to people on TTOL. I always handled all the paperwork, provided the standard TMM contract and all the contact with the client was my responsibility. I kept TMM fully informed before the charter but once the clients arrived at the dock, TMM then treated them exactly the same as if the client had dealt directly with them all the way through.
I believe this is the way it works with all the charter companies other than Moorings/Sunsail.
We once purchased owner's time from a Mooring's owner. Moorings handled all the paperwork and arrangements. Only difference was we sent the payment directly to the owner. No difference in service at their base or on the water.