If you're talking about discount supermarkets (Aldi, Lidl, etc), then note you're not supposed to pack your groceries at the cashier, but rather put them back into your shopping cart and pack up by the packing tables behind the cashiers. This way, checkout proceeds much faster compared to almost all other countries.
Also Rewe and Real enforce this behavior. And I don't see anybody doing this. The next customer's groceries are mixed up with yours and everybody seems to be ok with that.
