What sized tank is it and what kind of filtration are you using?
If its that 20 gallon goldfish tank in the profile, then not just no but hell no without some great filtration. 1" per gallon is a good approximate
rule of thumb, especially when dealing with the more common "**pet smart" fish(this changes greatly with more advanced and oddball fish).
Do note, people here are way more experienced than some minimum waged pet store guy for the most part. There are exceptions but they are rare and usually working at a pet store is a side gig for them. People who do stuff at work rarely like to do it at home too, when I was a low voltage tech, my landlord couldnt pay me to run cables in her rental houses in my off time.
Here you have quite a few hobbyist breeders, a couple commercial breeders, reefers who know more about water chemistry than quite a few chemists, and a few tech junkies who have tried every new gadget on the market for their tanks. Faced against some guy out of high school working a minimum waged job and told by his boss to selll stuff and really not worrying too much about it since it isnt his tank, the people on this board(and other similar boards) will out knowledge as a whole any pet store out there. Not to mention, who is getting your money and has the most interest in doing so? So when a consensus tells you something, they probably are more right than the pet store. **a better than my normal term of endearment for the super common, bread and butter fish commonly sold at Pet Smart, PetCo and pretty much every other mass retail pet store out there. You can usually find many of them at private pet stores as well at a slightly higher price. Yes, even my beloved Harlequin Raspboras I would count as a trash fish.