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?
Comments
Lots of times when larger collections get stolen, they end up going to fencing op's, who then use different people to do the selling at various locations who are not actually the thieves and have marginally clean records, so as not to attract attention.
Many times, a few pieces sold here and there, dont attract attention or suspicion in one specific place of business
That's what happened in the case of Vermont shops that bought English sovereigns and other bullion gold coins from young people fencing over $100K in coins stolen from an older man's property; he was found under a farm tractor dead. The estate led by his brother sued some of the shops to recoup the losses, fortunately one of the shops in Burlington had insurance that covered him.
https://www.vtcng.com/otherpapersbvt/news/police_blotter/coin-store-owner-admits-guilt-in-record-keeping/article_aaa3ac81-54ca-59d9-9df3-442202e48138.html
https://www.sevendaysvt.com/vermont/are-precious-metal-dealers-cashing-in-on-vermonts-drug-epidemic/Content?oid=2295784
If he walks into the shop with the goods in a pillowcase ...
Don't laugh. During the great silver run-up of 1979-80 this was not a rare happening.
Often, not always, thefts of large collections - particularly with an abundance of gold and silver, have pre-determined paths of disposal. Rare coins, value being way beyond bullion, are more difficult to dispose of - often such thefts are either by amateurs, who just do not know about coins, or professionals who already have a buyer. That is not to say that punk thieves do not steal gold and silver, and those are often spotted during disposal. Cheers, RickO
lets not educate the crooks to much here...........................
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You mean they are stealing pillows?
The police can take that down and use it as evidence! 🤣