I always get concerned when tradespeople express to a customer that they're 'fed up' - to me it implies they are frustrated because of their lack of patience, and it can reflect in the end result - and because of the degree of frustration they often think the price should increase due to their lack of patience and/or skills.
I have to say I have never met a tradesman who does exceptional work to behave in this manner. They get on with the job and complete it. when it's done, they usually quip 'wasn't one of the easier one's we've had to do' but they appreciate the praise for their effort when the compliments are forthcoming. They also don't rush work. The ones who do, are cutting corners.
My experience with the ones who complain about the job have a 100% sub-standard work for the $$$ paid. I could list a number of jobs on several cars over the years where this has occurred, and I've had to have the job redone by someone else. They are the ones I tell people to avoid, show the enquiring minds the examples of the work completed and the price paid. These tradespeople are usually the same asshats who say it will cost $$$$ because the badge is mercedes, and because you cannot find an alternative or have a problem with parts availability or a time issue, you get gouged, or worse, the job is unsatisfactory and you lose the time or have to fix other things 'casualties of war' - i.e. damage to paint or other return-to-rectify work - especially when it comes to exhausts and clearances.
I think as we age, our levels of tolerance increase to a threshold, then follows the downhill curve to the point where it's non-existent.
I hope your exhaust guy was just expressing his frustration at the clearances he had to work with, and it isn't reflecting in his workmanship.
Fingers crossed for you
This is another one of those 'reasons' I don't let people touch or work on my cars without supervision. I have a basic expectation that a job should be done properly, once. It's not unrealistic - it's an expectation that if you are a professional, the attitude towards your work is reflected in the quality of the end product.