I think Nick and Sheila's prices will be set by the company they're in partnership with. Maybe the original prices were in euros and so the conversion came up with an odd 67p when the prices were first worked out?
Amber paid everyone on the money and so did Sheila and Nick apart from the overpayment to Foxhunter.
Derek's £28 underpayment was absolutely outrageous and I didn't hear his justification for it - because he couldn't justify it. Between £5-£10 off for his cleaning issue would've been adequate.
Whatever he was going on about the hosting was most likely a chip on his shoulder I reckon and it was irrelevant to the pricing anyway as none of the guests would even encounter Jane or Russell at the holiday park.
Edit: just looked and the franchise partner dosn't look European after all so forget the 67p comment. No idea