My method is this....i mentally calculate the price they paid for their parts and than i give 2 prices, like this
Your brake job is 489.56 with 24 month... all parts and labour warranty with our parts.
The price with your parts and our labor is 367.88 and there is no warranty on the parts... I think you would be better off using our parts and labor, wouldn't you?
Then they gladly return their stuff!