This @sshole does not work in Paris so unable to help there - but does think that our FBO does provide an excellent service and value.
If I use a facility and don't think it is value for money I generally tell the facility and remind them that there is competition out there and give them the opportunity to keep my business. Works for me - so why not tell the FBO that's peeing you off?
FBOs do have high overheads because airport owners charge them very expensive rentals. Many operators use fuel carnets so there is nothing for the FBO from fuel. Factor in staffing, heating and lighting, tea and coffee 24/7 and you can't provide a US type service in the UK without making a reasonable charge. We have to try to provide a good service and hope that it gives us the edge over the competition.