Pretty much every switch, every "contactor", every "plug" has a rating in life cycles. The typical Centronics Parallel Printer Plug
that was standard with computers
for so many years? Was rated for less than 500 cycles, i.e. unplug it twice every day and it would be unreliable by the end of the year--even if many of them beat that rating.
So if your battery switch was made by a good company, and used within the ratings supplied, and had no defects....they can tell you how many cycles it was good for but that generally is "an awful long time" for recreational boaters.
Some companies had a problem with switches overheating
, literally metling and failing. There have been product recalls, check your vendor for that too.
"When a piece of equipment
fails after someone has just worked on it, well......"
I feel the same way, but also note that if a piece of equipment has just been hanging on (i.e. case or contacts distorted from heat) sometimes "even the best butter" isn't good enough, any touching it will cause it to fail.
I'd double-check the job, check with the switch maker (for ratings and recalls) and if there's no easy answer--replace it with a heavy duty switch from a prime maker.