Service department did sloppy work and won't admit it!

I have never had any mechanical work done at Leith and after today's incident I expect I never will. I called for spark plugs for my Acura and the quote I received for each spark plug without any installation was $18.35 EACH! I called an auto parts store and for the exact same product, brand and quality I can buy them for $2.99...UNBELIEVABLE. I did expect to pay more purchasing them directly from the dealer like $6-8, but not $18 each. I would be spending $120 for six without the cost of installing them. I know another practice that they are known for claiming a vehicle hasn't been painted but when tested...they LIE! tests come out positive. More reason not to buy a used auto from them in addition to parts for any vehicle. THEY ARE A RIP OFF!