When we were looking at our trailer last year I pulled up a report on the VIN# on FAXVIN prior to traveling out to view the trailer. That site will show the history of the trailer and if any wrecks, etc have been reported. The info is similar to a carfax report for a used car if you're familiar with that. For us it just gave us some added comfort before we drove 600miles to inspect/buy the trailer.
I paid $9.95 for the faxvin report on our trailer. You could order the report for your trailer and then send a copy of it to any interested buyer. For a one time cost of $9.95 its a cheap investment if it helps sell the RV for you.