Nonsense. That may be the case with you but not with everyone. I own a number of shotguns that fit very well and have bought all of them online. Most modern shotguns "fit" most people most of the time. Adjustment just makes the process easier.
Respectfully disagree. "Modern Shotguns" come with hugely varying LOP, different shaped and height combs, different cast off (or straight) different pitch and more. You may be very capable of adapting to bad fit - but that doesn't mean they all "fit very well". Try before you buy is a major advantage the clubs have, that online will never be able to offer.