Hi Mick. I went through a stage of cleaning carbs in the U/S even if they did not need it, but was finding that I was getting more problems than acceptable post cleaning. Carbs that had primed perfectly prior to cleaning would not prime afterwards, and in every case it was the little check valve that was the problem. And, of course, most are not replaceable, so new carbs needed. Incidentally, these were all on Zama carbs. I prefer now to use carb cleaner and gentle air pressure instead. If the carb is rusty or completely crudded up I fit a new carb. Its cheaper in the long run IMO.
But, to be honest, most of my customer base is domestic, and a high proportion of my regulars are using Aspen now. Carbs that run exclusively on Aspen simply do not need to be checked unless there are signs of contamination in the tank (sawdust etc), in which case the internal gauze may need a clean. The diaphragms will be fine.
So my service prices are tailored for Aspen run machines, with petrol users being penalised by the extra cost of carb overhaul where required.
I guess every business runs slightly differently.