I can't tell you how much money I have saved by following this rule. It's unbelievable the variety of quotes you can get on the same service or item. For example, we needed new tires for our car...I called one place and it was $1000 for 4 tires, the exact same tires at the next place $900 and the third place $700. The exact same product, lots of different quotes.
I know my sister has done the same thing with car repairs, when she drives to Pennsylvania to visit grandparents, she gets her car repairs done there for hundreds of dollars less than it would cost in D.C.
Sometimes, you have a certain place you prefer to buy products, ask if they price match.
Start to follow the three quote rule, you will be amazed!