In the USA/FAA world.....FAR 91.501 is a good read for "sharing" one's aircraft. One feature whereby you can "charge" double the fuel cost for (the) flight makes me
nervous.
The bird I fly for one individual loves to gulp fuel at such a rate that doubling the fuel cost would be more than the FAR 135 profit, in most cases. (Profit? 135? WTF?)
Unless the "sharee" knows the "sharer" it is a lost cause if asked anything. Most "sharers" own their own ship....if in MX, call your buddy with his own ship not in MX.
NBAA used to have a good read about this. But be careful! This reg begs to be misunderstood, thus, a dark grey cloud over your head. Registered mail sucks.
Cheers.