This is what full tilt has done to people. If your SPK's fit fine and are in fine shape keep using them. That classic shell is a tough fit. Maybe they run a little small but for me that meant actually using the size I measure at instead of going down half a size or full size.
If you talk about fluctuating more than one shell size (one full size) you are either A. in the wrong size currently or B. about to buy the wrong size. When in doubt go with the smaller boot, they break in and it is always easier to make a small boot bigger than the other way aroud.
Sucks for your buddy no need to take on the burden yourself. Tell him to sell them here or somewhere else online if he doens't want to hold on to them for next season, theres always a demand for Full Tilts.
I think you are confusing the job of a bootfitter. They do indeed do some work to modify the boots and heat mold the liners but the first and most important part of their job is to get someone into the right boot.
First, issue is finding the right size. An easy way to do this yourself is to find a ruler with centimeters. If it doesn't have centimeters you're gonna have to do some math (hopefully its better than your writing skills) I think its 2.54 cm to 1 inch or just type it into google. The sizing on the boots is called mondo point sizing and is just measuring the length of your foot in cm's. So if you measure 28.5 cm's you should be in a 28.5 boot. Theres much more to get into but thats a conversation to be had at your local shop.