An idea:
In the USA, you (or any marketplace user on their own) could further verify accounts by using USPS signature confirmation with return receipt. Have them sign their name on delivery with a preshared key (which is returned to the shipper automatically by USPS when using this service). You could send them something unique (preshared key, image, etc) and have them post back here on pinside with that information.
You could also send a letter signature confirmation restricted delivery (must show govt issued photo ID, age > 21).
This might slow sales (3 to 7 day delay) if individuals are doing this themselves but might be worth the time and money [$2.65 (signature confirmation) plus $1.70 (with return receipt)].
If a scammer is bold enough to use their own address or to mess with another's mail (Federal offense) then nothing you do will likely stop that particular scammer. I guess this is like a lock on a door, it will keep the "honest" thieves out.