Well, some FR difference is to be expected between samples, though it should be minor if QC is high. You allude to gear that a common consumer would use - does this mean he was using low cost cartridges? I would not expect QC to be as high on a $60 cartridge, as compared to a much more costly unit.
Another (cheaper and MOST accurate) way is to use the same cartridge and install it on both tables(take care of the mass issue, of course) and record the output from each one to a high quality sound card. Then level adjust and time synch the recordings with an audio editor. Now use a software ABX program to blind test the samples.
-Chris