I do a lot of repairs and porting in the UK, I take a failed repaired saw personally. If anything I do doesn't work then I WANT it back to get it sorted.
Saying that, I have had saws in for porting that have had shot carb accelerator pumps, shot fuel lines, leaking seals, damaged manifolds etc with no note from the owner who only comes clean after you find the issue!!!
In a case like this, I would ask the customer to send the saw back, if I had missed something then I would repair it, parts would be charged, labour would not and I would make a call on the return cost based on the amount of work I had done for the customer and if he had been 100% honest on the condition of the saw he sent in.
Pretty simple as it is easy nowadays to lose a reputation very quickly. it is also easy to misunderstand a repair bill so I sometimes have to explain why the bill is more than I expected and am always happy to do this although I keep the owner appraised by text of any nasties.....pretty simple ethic of treating others how you would like to be treated......I get a lot of referral work for some reason
In this case, I would say the shop took it the carb was OK as the saw had failed for other reasons and the carb had just dried up and the needle may have got a bit sticky from standing. I would have stripped the carb, specifically to check the gauze filter but I am a fussy old S#d!