I went to a large bike shop recently to get good lock for bike and some alen keys. I bought cable lock as it's much more flexible and more practical for bike touring. All I really needed was a padlock, but shop didnt sell them seperately. They didnt sell alen keys either, only bike tools with alen keys on them which are fiddly to use and not very practical. I went to a hardware store for the padlock.
I Went to a reputable music shop to buy a tuning fork, arguably the best way to tune ones guitar at home. They didnt sell any, only electronic guitar tuners
Had bike serviced by specialist bike shop in preparation for my 700 mile cycle tour to Dubrovnik. I Took my bike back to the shop that had custom built it for me the previous year, so trusted them to get it right. The only thing wrong with the bike was that the chain had visibly stretched over the last couple thousand miles so the gears were not indexing properly and I was missing the odd gear. I asked them to sort the gears out.
A week or so later the tech called me to advise that I needed new chain, rear sprocket and front chain rings as all were worn out. (when you have new chain on a bike, the shop will always say you need a sprocket too) . I was reluctant to disagree but knew this would be expensive so asked him to just take a few links out of the stretched chain and reset the gears for me. He thought I was crazy and told me in no uncertain terms that the chain wouldn't last the trip - his actual words were: "That chain is about to snap at any moment!" He said as I left the shop. He could have at least wished my good luck and told me I'd need it.
I've since cycled fully loaded over 1500 miles including over the Alps and Dolomites on the same chain and sprocket. Yes, he was wrong - or was he just trying to sell me what he wanted?
Shops dont sell you what is best for you, they sell you what they want, and what they have, even if it isn't whats best for the job.