A friend of mine and fellow pinside member recently sold an expensive machine on here in the 10k+ range.
In doing so he supplied character references to the potential buyer as part of the process. Basically he gave the buyer the contact information of 3 established pinsiders who know him personally (myself included) that could vouch that he did indeed own said machine and it was a legit sale.
This probably won’t work for the random person just selling one machine. However anyone that’s been around a while shouldn’t have a problem supplying this.