One drop of water can ruin your watch .
I do the battery changes myself. (ok, have to admit..I have a vacuum and pressuretester)
I am pretty picky in these items and have seen to often that gaskets are not placed accurately and the watch will fail a waterresistance test, not even a 1 meter test.
I am not sure about this but I guess the stores who do the quick battery replacements often don't know what they are doing. They don't perform any waterresistance tests.
A good watchmaker does know what he is doing and is worth the money in my opinion.
I never heard complains about the Citizen service centers, obviously as a lot of people use the promasters as real Dive watches.
You can take the risk with a 10 pound watch, but with expensive watches ..I wouldn't take the risk.
Something else with batteries, often overlooked..when a quartz watch runs out of the battery, replace it as soon as possible or take the battery out. Empty batteries can leak and damage the movement.