One customer remarked that one day I'd appear in a suit sharp enough to cut - and the next day I would be like a deckhand off a tramp steamer.
The answer to the paradox is that the suit was for first visits - the informal attire was for comfort when working very long hours to solve their problems.
One day the customer's senior manager confronted me on arrival about the poor reliability of the product I had come to fix. I agreed with him. His underlings told me that he took several days to recover from the shock of a "suit" agreeing there was a problem. Needless to say I always fixed their apparently intractable problems. If you dress like a techie - you have to deliver the goods.