yeah, that works in shops where you can talk to the owners. they will actually appreciate not having to use their bags since that saves them money. but in large supermarkets the employees usually don't have the courage to deviate from what they are told to do.

or it's simply not practical because the scale is not close enough and i'd be blocking it for to long. on busy days there is often a waiting line to get stuff weighed. so really this only works if the shop expressly designs for reusable containers.