My brother has just called me with an example - perhaps not brain fade but pretty damn stupid all the same
He's been called in to replace a wetroom that he fitted about 9 months ago. It was a very expensive job, all polished marble - floors, walls, the lot.
He's been called back because the people in the flat below were complaining about water leaks from the wetroom above. On inspection, the the wetroom was leaking - like the proverbial sieve. The polished marble was now matte, pitted all over and actually holed in places!
The (very wealthy but excruciatingly dim) owner had been cleaning the marble with an acidic cleaning product with the warning 'NOT FOR USE ON NATURAL STONE' in big letters all over the bottles.
She told him she didn't know marble was stone.
(Captain Placid 24/7 ball gags, brownie mix and clown porn, Fri 22 Mar 2013, 15:07, 3 replies)

i fit luxury bathrooms too
ive had people try to clean Dornbracht brass wear ( ridiculously expensive) with viakal and wire wool then totally deny the scratch marks are anything to do with them. They will stand there and say i just used a wet cloth while the viakal bottle is stood on the window sill behind them. Twats
(boarders You won't catch me with my trousers, Fri 22 Mar 2013, 19:36, closed)

Well, there's no such thing as common sense.
One of my brother's favourite jobs is replacing limestone tiles that have fallen off due to having been originally put up with acid-based silicone.
(Captain Placid 24/7 ball gags, brownie mix and clown porn, Fri 22 Mar 2013, 20:22, closed)

Yes
I've seen the same thing in the use of everything from old fashioned duplication machines to hormone selective weedkillers.
(Redemption blamed it on the Bossa Nova since, Fri 22 Mar 2013, 20:20, closed)