Someone posted before that a currency checking pen can be tricked and I was curious how - I read that a forger can bleach a lower denomination bill and reprint it is as a larger bill to trick the pen, and using a UV light to view the fibers in the paper was recommended. Each denomination has different colored UV fibers.

It seems the vertical strip inside the bill would also identify a washed bill since it is in a different position for each size bill and the denomination is shown on the strip when held up to a light.

Fortunately I know lots of pinheads locally through tournaments and such, so buying and selling is relatively safe with folks I know.

In the case of the robbery previously mentioned, the thieves used fake names, burner phone, and arranged to meet the victim in the parking lot of a commercial building where they claimed the fictitious pin was stored. The victim noted there were some red flags but didn't follow his gut instinct.

When reporting the crime to the local police, they suggested in the future to contact the police beforehand and they could meet at the purchase place to insure things are above board. Not sure many police offer that service but a call to the police non emergency number would confirm.

I recall the victim told this story on an episode of Kaneda's Podcast years ago.

More options I consider safe -

Buy/Sell your pin on the freeplay floor at a pinball show. No going to a stranger's house or having a stranger come to your place, etc.

Buy/Sell your pin to your local distro. Most are looking for trade-ins of popular titles and they have trade-ins for sale. Sure you will loose a bit on the transaction buying or selling because they are a business with overhead but if you're shy about dealing with strangers then this is a good option.