The renter has no control over the quality of maintenance of the
plane, how previous renters operated it, or many other factors that
could lead to an unexpected breakdown.

The position of the FAR's and the FAA is that the renter should not be
flying the aircraft if he feels he or she has not control over the quality
of the maintenance. According to the responsibility placed on the pilot by
the rules, the PIC should have reviewed the logbooks, inspected the aircraft
thouroughly, and performed some due diligence that the shop was on the up
and up. I you come to the FAA's attention because of a mechanical failure,
or possibly even a ramp check, they will inquire when and how you did these
things. If you did not do them, they may take your license for a while. If
someone got hurt, failure to have verified these things will be blood in the
water for the lawyers.

These are not rental cars. Your responsibility goes far beyond what 99% of
rental pilots live up to.