What to look for when stolen material is being sold?
I got a call last week from someone who was selling Proof 69 and Proof 70 1/4 oz and 1/2 oz certified NGC and PCGS gold coins. What was suspicious is that he did not know what he had, he didn't say "proof" or other normal verbiage for a collector. I mistakenly gave him a ballpark figure on a 1/4 oz eagle not thinking based on the denomination on the holder, he said "$25 G" was on the holder which in reflection corresponds to the 1/2 oz coin; I figured it based on gold price plus a little. He said he paid more than that so I corrected myself. The fact that he did not know what he had made me suspicious though he knew he had gold. I did not get back to the guy who wanted buy prices.
A day or so later a couple from Maryland brought in a number of Unc. $20 gold pieces to a shop, they looked like Libs. to me. This is a Connecticut shop a couple hours north of NY. Later I asked the shop how they screen out potential theft. They said in 20 or so years they have only turned away a couple potential sellers. And they said that the police don't usually match up IDs with material sold unless they have a specific report of theft definitely tied to someone.
The difficulty of screening out potential thefts with larger numbers than usual is concerning. What should people look for in suspicious selling activity?