As long as the pilot (PIC) pays an equal share of the costs (or more). You must avoid the situation where the pilot gains anything financially by taking passengers. If the flight were a lesson with an instructor then the instructor would have to agree and of course all subject to weight and balance.
If you are a pilot who would like to offer another pilot or student pilot the chance to fly with you on a cost share basis then we have a notice board for this very purpose in the flying club where you can place your offer.
Offers like this are very welcome!