I did parts for over 30 years. Had one store owner offer me a position with a sliding percentage depending on sales volume. I asked him why he wanted to hire someone that would only give their all if they were paid extra, and why he wouldn't pay for experienced parts help that could do the job day in and day out without f-ups. Needless to say, I didn't take the job and the guy never contacted me again.

I could go on about parts sellers and dealerships that front load their costs. Those are only accounting tricks to make it look like the dealers aren't screwing the sales force on their percentages.