I saw this product at SEMA, a good investment if you buy and sell cars. Amazing demo, it finds filler and even tells you how thick it is. Helps you make a decision to buy or not, or negotiate prices if you find filler and still want the car. You can also use it show potential buyers that the car you are selling his filler free. Less than $90, would pay for itself in one use.

http://fillerdetective.com/

Pat