And you're only allowed to cost-share up to a max of 4 seats IIRC.
You've opened up an interesting can of worms there ...
The rule appears to be :
(a) No more than four persons (including PIC) are carried
(b) PIC must may his proportionate share (e.g. 25% if 4)
(c) no information shall have been published or advertised prior to the commencement of the flight (except if a/c is owned by flying club, in which case it can be advertised in the premises of such a flying club).
The can of worms would materialise if you were to mix (c) with PPrune, for example ...
