Slim, I think that happens for one of two reasons ... some are just blatant sh*theads who simply don't give a damn that it's someone else's store ... then there's the others who (don't ask me how, I dunno, but somehow) space out and just don't make the connection that the BB is contained within "someone else's store" ...
the latter group needs only a reminder to cease and desist, while the other bunch couldn't be cured if you swatted 'em with a 2x4 smack between the horns ...