No problem, I got that it was stores you meant. What I don't get is what customers do if they once get a canister from them: Now they have two. Can they return

No problem, I got that it was stores you meant. What I don't get is what customers do if they once get a canister from them: Now they have two. Can they return the extra for a refund in stead of replacement, at one of the "normal" places that does receive used ones? Or are they stuck with two canisters for ever more?