One very bad idea is for an optician to display rimless glasses on a glass shelf.
When a customer takes off her own glasses it makes seeing the above difficult.
It is easy however, to pick up the large hand mirror and accidentally bash the invisible shelf quite smartly....
It is then advisable for the shortsighted customer to stand very still while the receptionist picks up all the rimless glasses and tries to find the ones the customer was wearing when she came in.....☺
Very bad advertising, seen in a beauty shop window in Torquay before we moved up, which purported instant tanning, and beneath the "instant" tanning turned out to be a fifteen minute job!
I know what people are going to say, but "instant" should have been replaced with "quick" tanning, in my mind.