* I don't know exactly how such a locker works and whether OP cannot pick up the item, tamper it and then "post it" to another locker for the user (in my country the lockers belong to the shipping company and multiple sellers can use it).
I've never used those lockers, but I assume Amazon designed it so that you can pickup your item, after which it's locked for the next customer. So you can't open it again, and I don't think consumers can send packages to those lockers either (that would enable drug dealers to use them).
An anonymous one-time use "post office box" would be really cool for anonymous deliveries though!tamper-proof selling to potential customers (to convince them in order to buy) is something you will probably struggle with.
Ledger doesn't even offer tamper proof packaging:
Ledger deliberately chooses not to use anti-tamper seals on its packaging. These seals are easy to counterfeit and can, therefore, be misleading.