2gph will fry your engine in 10% of its TBO
What??? You ought to get current with modern engine management.
Irresponsible, and why FBO's always rent wet. If renters paid for fuel, with a lower overall rate for the a/c, some dolts would fly with pistons pinging, enjoying their extended time in the air. Pilots are responsible in the great majority, but taking a chance on the odd nitwit isn't worth it, believe me.
IMHO, a far bigger reason for wet rental is (a) lack of training on the Red Lever in the UK PPL syllabus, and (b) that most rental stuff is clapped out wreckage without accurate (or any) fuel flow instrumentation so there would be no way to invoice for the fuel separately.