LOL!!!!!! Funniest thing I've read in a long time. Somewhere around 95% of all work LE is called to do is on the basis of a 9-1-1 call or a phone call to the non-emergency number of the department. Darn little of it is because of a complainant coming to the station or flagging-down a patrolman. Considering the size and population of the US, I'd guesstimate that 50,000 contacts are made by LE EVERY DAY in America based on a "telephone compliant." Good luck getting any lawyer in America to handle your suit, because they all know they'd get laughed out of court.

Why is this germane? Because you should not dissuade the OP from calling the police. That's what they're there for. IF this situation had happened in my state, I can think of three felonies the seller is potentially able to be charged with. The bottom line, though, is that if this is a legit deal and the guy is just lazy or has a genuine problem like being in the hospital, the police officer / deputy will investigate what is going on, and either resolve this issue with a prodding "get-r-done or you'll be arrested for not delivering the product you've been paid for" (a.k.a. Fraud and Felony Theft) or the buyer will get a call back from the officer stating, "spoke to the guy's wife - he's in the hospital (or whatever)." This is a fairly simple matter that is handled all the time by LE.

Only if the problem persists with no resolution should any enforcement action be taken, and at that point, it is certainly warranted. Another side benefit to calling the police is that someone trustworthy "all the way over there" (where the OP is not at) will be doing a face-to-face verification of legitimacy (or lack thereof) for the concerned poster here.

The hardest problem will be getting a local agency interested in something that occurred via commerce across state lines. They may question their jurisdiction and want to kick it up to the Federal Level, IF action eventually has to be taken. At the knock-and-talk level of finding out what's going on, the local agency should be able and willing to do something for you.

The letter idea certainly won't hurt, but at this point, it's not sounding like it will help, either...