i am looking at the message right now, it says " you can keep the brass metal, I am more interested in the private key and the coins inside so you can sell the unfunded coin for extra cash"
Feel free to post the screenshot of the message here.
In anyway, funded coins can be sold peeled or unpeeled but prices may differ, of course.
I'm sure there will be interested on old bitcoin funded on physical coin, coz it can be redeemed on different bitcoin fork which will have much value now.
Regardless of someone want to buy the physical coin peeled or unpeeled or just the bitcoin/private key, escrow is a must bot unless if you trust the buyer, but escrow is still recommended before doing the transaction.