Of course nothing is free, and we all expect to pay.
I much prefer a built in price rather than a charge per item invoice.
Of course a quick turn can be charged at less.
This is easy to bill, if the plane is there for say 6 hours with the crew mooching around, charge a parking fee etc... this covers use of the facilities.
The best FBO I use happens to be the one I'm based at.
No charge for ice, no charge for hot water, no charge for use of the crew facilities. Not just for based aircraft, but for all visiting aircraft.
There is also complimentary snacks for the crew.
Their prices are also very competitive.