Cost sharing when you have to re-position the aircraft

[GeeWhizz]

Realistically?

Only ever did one sight seeing trip for a mate that needed collecting from another airfield. We shared the cost only for the time he was a passenger in the aeroplane. I just did the trip on a day when I was going toward his direction anyway making 'ferrying' less inconvenient. I think this is the best way.

On the other hand, there's not much of a reason why a pilot (PPL) and a passenger (non-pilot) couldn't agree to share all costs for all the flying, inclusive of the ferrying between airfields.

Without opening up wider discussion, these arrangements are purely based on trust depending on pilot nav ability, distance between airfields, anything that may keep you in the air longer than necessary. These are all detrimental to the cost-sharing passenger. To agree full cost sharing including positioning means a higher portion of cost for the passenger for much less flying time.

I'd keep this sort of thing honest and simple, and only agree to share the actual passenger flight costs.