Paint Thickness Gauges?

I may be doing some car shopping in a neighborhood that takes me slightly beyond my Challenge-Friendly Comfort Zone. I'd like a little more reliable indicator than Carfax that the car has never had any paint or body work done. I've seen paint thickness gauges used, but I've never used one myself. So I'm seeking the opinion of someone with bodyshop experience. Are these things reliable? Is there any one brand that is better than any other or are they all pretty much the same?

I was taught the following method to assess for paintwork when I worked for Carmax a while back: Run your fingers along the edges of panels - like the back edge of the hood, the edge of the trunk by the rear window, door edges, etc. From the factory, these are 100% smooth from the factory because the paint is applied in ways where masking is not necessary. If the panel has had paintwork done, there will often be a ridge on that edge, created by spraying/masking/etc.

I'll add to the comment above being a former appraiser myself. Tape lines are a great first indicator, though Some paint shops are so good there may be no tape lines so take a bottle of detail spray and wipe the panel Down to look for any trash in the paint or runs in the paint. Usually I would "surf" the panels running my eyes up and down the panel at a 45-60 degree angle. Also pull weather stripping and look for signs of rewelds, I've had cars in the past that showed no signs of paintwork but had a rehung panel. Also look for bolts being adjusted. However a paint thickness gauge is a great final say in all of your assessing, but a little know how goes a long ways.

All the gauges I've seen are expensive. Which one would you be using? Might not be worth it for a one time use.