Again, it's all personal preference. If you have wide feet, you may need to get your boot stretched to fit your foot. Since most all skates are made with plastic shells, a good shop will offer custom molding to their customers. A salesman may try to get you to buy a bigger boot that would be wider, but don't do that. If the boot is too long then the fit will be loose and tend to cause blisters.
Narrow feet are a different story.
The easiest way to deal with them is to add pads in along the liner. Underneath, on the sides, wherever you can to make a good fit. And of course like in the wide foot, you don't want to buy a more narrow but shorter boot. Don't trade one uncomfortable aspect for another. Realize this when you talk to your salesman as he can fit you best.