I used to do a lot of business with DT, but have found that their prices are just too high, even factoring in their service level.
A year or so ago I came to this location to purchase 4 new tires. I knew that DT will price match with their competitors and even with online tire sellers, so I had in hand a printout from an online competitor - same make/model/size as one they had in store. The employee I dealt with looked at the printout and in their computer system and started to give me the stinkeye. He went on to say they don't like to match online retailer prices, but they will take the online price + shipping, add tax and then sell me the tires at that price (DT would then add 8.3% AZ tax on top of this amount). If they did that then I'd only be paying about $2 less per tire than DT's normal price. I said no thanks.
Then recently I was looking for 4 new Michelin tires. I priced out a set of Primacy MXV4s at DT with the tire warranties minus a $70 rebate that they had running at the time. Then I took this amount and shopped around. Practically every other tire shop was cheaper for the same tire set (including a road hazard warranty). I ended up getting the tires at Costco and payed $200 less than DT quoted! $200 less at Costco's normal price! Plus Costco doesn't charge extra for road hazard warranties, and will do free rotations/repairs just like at DT. I suppose I could have showed the Costco price to DT so they could match it, however they probably wouldn't have matched Costco's road hazard warranty price ($0) and who knows if they'd play games with adding on tax, or the price of Costco membership, etc.
One thing DT has against them is that other tire retailers are starting to include road hazard warranties in the price of their tires while DT still charges extra for them.