Down the line if your address was exposed you could claim to have stuck them back in the mail unopened with return to sender written on them?
I wouldn't like to be relying on that though.
However, for recreational consumer use, you're talking quantities that absolutely could not justify such an operation. The value in such an operation through a traditional drug dealing network would be that the person caught could serve up information on who they got it from. When you're talking about buying drugs anonymously online, none of that information will be available.
And wouldn't you then be into amounts exceeding recreational amounts?
PM is €3-€4 for a standard package, so what I'll regularly encounter is things on Amazon that are free delivery to the UK but quite a bit more expensive than PM to be delivered to Ireland.
Things also seem to ship through PM drastically faster than through the normal postal service.
The real criminals will have the stuff delivered to some poor unfortunate who they've scared witless and not worry about the minutiae.
But you make a good point - if you are going to invent a name, you should probably choose one of the previous occupants.