The business model of the independent tire stores!

There are 2 independent tire stores in my town. When you get a flat tire and take it there to be repaired, of course you expect to pay for it, but they always say "it's on the house". Sure is nice of them, right?

Last year I bought six 16.5" Firestone Transforce tires for my dually from Walmart because they had the best price and claimed to offer free installation. However, they refused to install the tires because they were an "odd" size, and there was absolutely nothing I could do about it (did you ever try complaining to Walmart?), so I took the wheels and tires to one of the independent tire shops and asked them to install and balance them, expecting to pay a pretty stiff price for all that work, but they AGAIN said it was free! So at this point I was thinking I was their friend for life, and would buy all my tires from them in the future.

Then I called them to see if they had any 235/75-15's for my van, and their prices were $100 per tire more than Walmart and $75 per tire more than America's Tire. (America's Tire is probably the most professional and reputable tire chain around here.)

So are we starting to understand the pricing business model of the independent tire stores?!