We had someone do something similar. USPS inspectors got to the bottom of it and made the miscreants pay for postage as they were just stuffing them in mailboxes which is illegal. I believe they were given the option of paying or going to prison for unlawful use of postal property.
The wife and I just got back from grocery shopping at Lowes. We spent a bit more than usual. I don’t think there was more than a dozen other people in there. It was nice and quiet and for once, 2 checkouts open was enough.
Terry