Go to a "social focal point" in your town and look for a house with many flats the kind they put welfare people in. One where the front door s always open and access to the mailboxes is possible. You will find a good part of the boxes destroyed, door ripped open or off and its a mess. Grab a mailbox,repair the door and fix a lock similar to other mailboxes there in working order, nobody will give a fuck. Put three or four names in the box. And thats it. check and repair as needed.
And thats your return addy. Which you need. A working return is essential and the return must be on the envelope and the goods should be in a secind enveloope which also has the return on it.
In Germany most vendors get caught because they use random returns and the customers in their paranoia fuck up and the stuff ends up in a random persons mail or at the place where they open the letters to try to find an addy to return there. And so the pigs get involved and as those are highly staffed and paid and motivated special units not the usual corrupt local policemen who have own biz to tend to, the vendor will be tracked down and royally fucked.