Many people buy the wrong sized pack; both in volume and torso length.
Guilty! A couple years ago I bought a $450 Mystery Ranch pack and didn't really pay attention to the sizing. I wanted a large waist belt but I ordered one with the XL yoke!
Didn't try the pack out until the return period was over so I got stuck with a pack that I can't adjust down to get the load lifters right. The good news is I finally sold the pack...for $125!
I'm taking it to the buyer tomorrow. And expensive lesson!