You may suffer from a common affliction called Haglund's Deformity (I do). It's a bony protrusion on the heal, and it makes getting proper-fitted boots somewhat difficult. The symptoms are a local hot spot (it'll turn red) on the outside of the heel. For me, it never manifested as a blister - just a serious amount of pain during hikes.
When I started backpack hunting in steep country, I did a lot of learning about foot comfort. When you are carrying a 50-100 lb pack for 10 miles a day or more, ill-fitting boots aren't just an inconvenience. If you have Haglund's Deformity, boot choice can be limiting. For daily wear, though, it's much easier to deal with; however, when you're spending $500 on a pair of mountain-capable boots and they don't fit, it's a PITA because by the time you figure out they don't work, the manufacturer won't take them back. I spent thousands on boots, and hundreds of miles of training hikes, to find the right pair (Kenetrek Mountain Extremes).
For daily wear, I alternate between my Red Wings (mainly winter) and my Salomon XA 3D Pro trail runners (mainly summer). The Red Wings finally conformed to my Haglund's bump after a couple months. With the trail runners, the Haglund's bump wears a hole in the liner and into the padding, which gives clearance. Those shoes wear pretty fast, so the liner hole is never the reason I replace the shoes (the tread wears out or the soles delaminate). I get better wear out of those Salomons than any other sneaker I've tried, but I still think they could be made better when the delamination occurs before the tread wears out. I'm on my fifth or sixth pair of them now...
