BP... I used to rent out my TB20 and got these various issues.
I used to rent out DRY and (not sure if you know how the UK duty drawback works) it was manifestly unfair to other flyers when one flyer (renter) pocketed the drawback following a 30min flight to LTQ. The drawback paid for his whole trip, but of course that was subsidised by all those flying before him, on any part of the 86USG tank capacity.
The scheme, before I changed it
, created an incentive for somebody to come along once a month and do a very short flight abroad, which cost them approx nothing. (Curiously it was 2
instructors who used to do this irritatingly in-your-face stunt
).
One alternative is for (this not really applicable to pure rental) the drawback to go into group funds. The particular flyers won't be so happy because they pay the same wet rate as the others (most groups have a WET hourly rate, partly due to lack of fuel flow instrumentation and partly because the members don't fully trust each other to not fiddle it) so ideally they need to be offered a slight discount on that. But that discount is applicable only if the drawback is untainted by previous (and too-recent) foreign flights, otherwise it gets complicated to work out. But if you don't offer any discount on the foreign wet rate, the foreign flyers are subsidising those who don't fly abroad, and since they will generally be the bigger spenders within the group.... you get my drift, nothing is perfect.