I like the direct, and assertive approach outlined by a couple of the guys above. Shoot 'em down early and then get back to work.
As for the silly games that you play on the telephone, or in the office...how much is that really costing you? How much are these rants costing you? (Shop rate x ? hours on the telephone / forum in an average week or month = lost profits)
You'd be pissed if they came in and snatched a $50.00 dollar bill out of your pocket every time this happens, but hey...that's what they're doing.
Hobby or business? That's your decison.
JB