I think you have to differenciate between "club" check-outs and "required by the regulations" check-outs or training flights. If it's just for the club's own regulations, then the pilot, not the instructor, is PIC and thus puts it down in his book accordingly... whether the instrutor gets paid or not.... unless the club designates in writing that for this particular flight the instructor is PIC. All "required" check-out and training flights, like the one for revalidation, the instrutor is PIC. The same with flights with an examiner.
That's the way I see it.
We have people writting down times (though not PIC) when they are in the right seat claiming they helped with the radio work or navigation. They don't realise that normal single-engine non-commercial flying is only required to have ONE pilot on board and thus they are to be considered passengers. I even heard of a guy writing the times in his logbook while he was flying in the rear seat!
aw, come on now....
Westy