I've done a fair amount of boot shopping over the years and have always heard the same story from every shop where I have purchased boots - we guarantee the fit, any problems, bring the boot back in and we will adjust it. Little or nothing is ever said about what will happen if the boot just can't be made to fit. My own experience has been that once that point is reached, you are just SOL, and it's either ski with the pain or buy a new pair of boots. Won't go into a long re-hash of my experiences, but that's been what I've seen - 'we guarantee it up to a point, after that it's your problem'.
Last year, went back to a local shop with a good reputation for boot fitting. Took my son in for a new pair of boots, looking for something high-end, a bit more race-oriented. Was getting on in the season, so there wasn't much left in inventory, but we found a pair of Technica's, and, although I was skeptical about the size of the boot (thought they shell sized him too small), he reported that they felt fine in the store. Different matter on the ski hill. Couldn't get more than a couple of runs in and he was in agony and heading for the chalet. This lead to weekly visits back to the shop to tweak the boots for the remainder of last season. Nothing seemed to help, but the shop put a lot of time and effort in, punching out the shell, etc, etc. Got to this year - first day of the new season - same result - one run and done. Once more back to the shop, but this time, it's the shop (rather than me) that says 'We're done here. Nothing more we can do to fix this boot. We will give you your money back and let's look for a different pair of boots.' So, we 'returned' his boots and bought a new pair. At the end of the day, the money out of my pocket was probably about the same if the store had just blown me off as other stores have done to me in similar circumstances, but it was so refreshing to NOT to have that argument.