We have a great mail carrier and alternate carrier now, but it wasn't always that way. At one time while I was selling on eBay, two payments mailed to me in properly addressed envelopes were returned to the people who sent them, stamped "No such address."
One of the buyers enclosed the envelope that had been mishandled when she sent payment again. I took that envelope and an email from the other buyer with me to the main post office and filled out a complaint form. We had a different carrier on our route very soon.
The funny thing was that she must have been mis-sorting lots of mail, to have enough left at the end of the route to justify buying a "No such address" stamp. The postmaster said it wasn't issued to carriers.