OBD AND ECU SCANNERS.......

I want to buy a competent handheld scanner that can basically mimic the functions of a factory unit to the extent that current laws allowing the sharing of propietary technology will permit.

Here's my problem..........most OEM scanners either get locked out of the ECU, or can tell if the ECU has been flashed. I need a handheld unit that can register this as well for when I am appraising units at the auction before I bid on them. If you buy a car or SUV that had an ECU flash previously, the manufacturer commonly will void the vehicle warranty, which obviously will significantly affect the resale value if it is a relatively newer piece.

Does anyone have any recommendations ?