Never, and I can usually conduct my business without making noise or touching any gear at all. However, there have been times I've told 'customers' to stop playing, when the clerk wouldn't. They always stop, too... I guess I don't look very friendly.
Bermuda
Its a drum shop, drums are made to be hit, its there reason d'etre. If the phone goes they may ask you to stop, but that is obvious. If you are abusing an instrument they would probably ask you to stop, but I have not seen any problems during my, frequent, visits.
On the other hand, I was in a big music shop in Leeds, with a big drum department, and the whole shop was plastered with "Do not touch" signs. What sort of message is that to send out to a budding drummer?
Those signs exist because people come in and just thrash away at gear. They're not usually budding drummers, and they're not customers, they're just making noise and causing wear & tear on gear that they're not going to buy...
There's no reeason whatsoever that people should be playing drums in a store if they're not trying them for purchase.
Bermuda
Thrashing on drums in a store is analogous to taking a car for a test drive, going off-road, and bringing it back dirty and beat up.