Never let a salesperson push you into anything....particularly skiboots. You're the one who makes the choice...aggressively or passively. Most of us have made a wrong choice at some point in time..... Maybe I'm a little too gung ho about doing most of the shopping yourself...my heel, lower leg, ankle fit a #24 shell perfectly, but need various areas of volume.
Lots of shops won't order a #24 unless a purchase is iminent = Just Greatuke:...LOL...but the unending sagas teach what to look for in a boot....I think.....ie Atomic & other bootmakers don't even make certain models in a #24 shell... Maybe they don't really make the boots!..y/n?, just market them.
I went in asking for a very particular boot. My prior boot was a similar version, which they carried, from the same manufacturer. They did try to push me into other boots they had in stock, which I can tell you did NOT fit correctly. I remember one in particular that was way too low and loose around my lower leg and calf, but still, they were pushing it on me, presumably since it was a prior year model they wanted to liquidate.
After I determined that I did in fact want the boot I went in looking for, they shell fit me with the similar model, which has the same last. After the whole debacle, I still ended up with the same boot I bought, just a size smaller, and I couldn't be happier. To your point, I know that much more about shell sizing now and will not repeat that mistake.
I do hope my experience was a one-off, and that others, including those who have posted here, continue to have a good experience with them.