All,
Obviously some finesse is involved in using this method. I generally wait until the seller is ready to take the money and then I say,
"Do you mind if I swab a small part of this piece with a cotton swab before we finish the deal?"
The swab is in a small prescription bottle already moisened with semi-chrome, which I have secreted in my pocket or Gun Show bag. I simply pull it out and then explain slowly and carefully what I am doing. I can generally tell by the facial expression whether the guy is "Knowingly" selling a boosted gun.
If he hesitates or refuses, I politely end the sales transaction and simply walk away.
I have never had a problem with this and the amount of surface to be swabbed is so insignificant that the likelyhood of two or more collectors removing ALL traces of oxidation are extremely remote...about as likely as my voting for Hillary or Hanoi Jane.
Tom A. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />