Here is the secret to wholesale tires. The more you buy, the cheaper they get. It does not matter brand or style. For the big shops/mega malls/online stores who buy tires by the semi-load, the discount they get is huge. So much so, that their retail price is less then the wholesale price a small shop would pay.
So it's not that the small shop is overpriced on tires, they just can't get them for the same wholesale price as the big guys.
The same goes for OEM and aftermarket parts, but not to the same extreme.