> What percentage of Bob's customers bother to do that?

Would these people use a cleaner solution anyway? I mean, you can say that of any refilling system, if people don't use it.

It's more difficult if you have lots of special containers (in this case with integrated electronics) that can only be sent back to a specific shop.

My dishwasher uses detergent powder which comes in simple plastic containers that can be dealt with via regular plastic waste collection.