A problem in a large shop is the actual part R&R is turned over to a Wrench ..[ My Dealer/Tech friend calls them "Z-Techs".]
A thru Z... "A" being great and "Z" being the new kid..

"Give this one to one of the "Z Techs" ..

So, the car gets diagnosed by someone who knows the Tech end, but the part gets changed by a guy who doesn't..and you wind up with a set of installed fans that run great, but backwards.....