Quite agree with the "doughnut" method - I've used it myself, although not to the extent that DZL LOU has taken it!
The "doughnut" method could be a generic term as well for cultivating a good working relationship with your dealership/garage of choice. Something as simple as letting them know you'll recommend their business by word of mouth to others, or that you'll give them repeat business, because you think highly of the way you've been treated and the quality of their work, can go a long way.
One recent personal example - Earlier this week, I had a set of Cooper tires installed by a local dealer. We've purchased several sets of Cooper tires from them over the past two years - the tires have given excellent service, the personnel at the shop have been more than friendly and are quite good at their job, they've offered very competitive prices, and they've been more than willing to take the time to discuss different ideas and options for tires on our different vehicles - no hard sell or trying to push the monthly special. On this trip, we spent nearly a half-hour BS'ing about CRD's and other diesels before we got around to actually putting on the tires, and was invited to come back into the shop area to continue the discussion as they were rather curious about this diesel powered Jeep.
The stock Goodyears had 25K on them, I had a rather low opinion of them after recent experience, and knew they didn't fit any of our other vehicles (not that I would have put these POS's back on any vehicle driven by someone I considered a friend). So I let them keep the tires for disposal.
For that matter, they had quite a pile of used Goodyear Wranglers in various states of wear stacked up outside - matter of fact they constituted the vast majority of their removed tire pile. IMO, that spoke louder than any reviews on tire rack or other sites concerning the quality of those tires!
Later that day, my father had a coniption fit when he found out I'd let them keep the tires. In his view, they still had good tread, and he could have sold them to one of his friends for some pocket money. He even tried to get me to call the store and tell them I wanted the Goodyears back! Fortunately it was past their closing time.
Next day he made a trip into town, and when he came home 3 hours later, he had 4 used Goodyear Wranglers in the bed of his truck! He'd actually went by their shop and demanded the tires back, even though they weren't off his vehicle and legally he had no claim to them.
But the joke was on him, as the kid he'd dealt with grabbed the only set of used Goodyear Wranglers left there (they'd already shipped out the discarded tires from the previous day) that were off a vehicle with 15" rims.
That didn't deter him, he went back again the next day and tried to swap out the 15" tires he'd gotten for what came off my CRD, and was rather irritated when he found out they'd already been disposed of. When he got home, he was making comments to the effect that they'd tried to cheat him in some manner, and I could imagine the comments he'd make about this shop to other people.
Knowing how my father is, I could imagine how he might have dealt with them face to face. I called up the manager of the store, explained the situation as I understood it, and apologized to him for any interruption or inconvenience my father might have caused.
Botom line, I had a good working relationship with these people, and I didn't want my father's desire to get something for nothing to put that in jeopardy, so I called up and offered an apology.