I found when a seller became elusive when I had paid for parts but not received them that mentioning that his details, the transaction details and copies of correspondence were of interest to his LOCAL police who took a dim view of fraud/theft the seller suddenly became quite chatty and apologetic. My gear showed up pretty promptly.
Like LWC,you have to make the recalcitrant pricks understand that YOU CAN REACH OUT AND TOUCH THEM (whether in a 'polite' or even a particularly personally unpleasant way) despite where they live.