I have a buddy who listed his Porsche on the Market a few weeks ago.
He had two potential buyers pay for a PPI first then look at the car (the're doing it backwards)
PPI went very well at both shops and the first guy got cold feet because the shop could not determine how many more miles the clutch would last and the second guy only drove a 996-Tiptronic and wasn't so sure about driving a manual.
The shops were very happy to collect the buyers money.
If was going to sell mine, I would just list the car and keep driving instead of letting it collect dust in the garage.