I'd be very unhappy if this had happened to me, whether or not it caused light problems. Not sure whatyou were having done to the camera, but, if it were for attaching new coverings, my guess is that this is some kind of dried cleaning solvent, producing glue residues. I would certainly complain immediately; if you used Paypal or your Credit Card company, they may be able to help.
I've seen similar problems happen in other areas, where someone starts a small business, perhaps part-time, and perhaps undercharging. They get overwhelmed with work, start to take too long, standards of work fall.........