If you own a pet store, would you let visitors take photos of your pets?

That pet store owner is definitely short sighted in my opinion. People might be deciding if they want to buy sometime or not. Treat them nicely might help them make the final decision on buying. Even if someone does not buy anything today, he or she might come back later in the future. Photo taking is indeed free advertising. Virtual advertising is far superior than word of mouth alone.

Flash should be turned off for sure. I see no ill effect without the flash.