Can a person (even if they dont live there) sell on another persons res if they give them build rights?
Yes, but container perms are far from ideal. I use a very simple and easy system - The seller has temporary build perms in my presence to set up their chests and signs. I use the [access] signs to let them re-stock, then remove their perms once they're done. It's not ideal, but at least 100% theft proof. It depends on how many people you want to have selling on the one residence.
Can't you just do a double chest, with one side setup as the shop (which requires short term build permissions) and the other side with an access sign for them?