First, make sure you have the customers permission to do something like that. Nowadays, with all these whiney people you never know who's going to throw a fit and for what reason.
And when a customer asks me for a test spot, I do it on the hood, or decklid.
Yes but should we be forwarning them?
Best place to keep them from complaining about it.... on the back where they can't see it.
Best place to keep them from missing it EVERY SINGLE TIME they get in the vehicle. Do one about a foot square right in front of the left windshield wiper, another on top of the roof where they get in, and a third at the front of the rear quarter panel beside the drivers door handle!
Thing is... if you don't make it ABSOLUTELY clear that the 'test spot' IS going to change the look of their swirled out, RIDDED OUT, totally neglected and ignored paint so much that it looks like it's been repainted, then once you do the spot on the hood.....
You're likely to end up doing the entire hood to get them to shut up about it. (FOR FREE)
But it they ASK ABOUT IT, and you've made it clear (in writing on your inspection sheet) then you want to do it where it'll get the most attention. That'll hands down be a horizontal surface, and the hood is where you'll get the most benefit. :dblthumb2:
I just don't do them though unless it's in writing that I'll not do the rest of the vehicle.
The owner needs to understand just how much work goes into a paint correction, and unfortunately hardly ANY do. :dunno: