I also use AlphaCars on RT111 in Boxborough. Very reputable independent shop in the local community, and I've found them to be an good alternative to a big dealer. They do great service work on vintage and newer cars and offer many interesting late-model luxury vehicles for sale. Their specialty is Mercedes and BMW, although I have had them service Audi and I know they also handle jaguar, vw, porsche, acura, infiniti, etc.
My father has purchased a car from AlphaCars, (and it was a very good experience), but I have only had the chance to use their service department. I have been impressed. For an independent business, their service facility is remarkably clean and the equipment is state of the art. In addition to the mechanical service area, this facility includes body shop and detailing center. They repair cars promptly using only OEM parts.
As I mentioned, my father recently bought a car through AlphaCars. He was approaching a big birthday, and he felt the late-midlife-crisis-mobile calling to him. He saw several Mercedes on the AlphaCars website (www.alphacars.com) that interested him. Dmitry showed him a CLK55 AMG that he liked very much and a few E500s. In the end, old man went for a pristine and loaded E500 4Matic Wagon, which was gently used but significantly marked down from MSRP. He aquired what is basically a $70K new Mercedes for half the price. (By the way, try the dynamic seats). It's nice to know that someone will take care of your dad when you're not looking! He will service the car at AlphaCars as well.
I most recently entrusted them with my '87 BMW 535i. I brought the car in because it was leaking coolant, stalling, and it needed a new thermostat. In addition to repairing the problems I was aware of at a very reasonable price, Alpha diagnosed several other issues and made recommendations with detailed estimate. I declined some of the services at that time, but now I know exactly what the car needs to be tip-top and how much it will cost, and when the time comes to make those repairs, I'll be using Alpha. I recommend them. Check out this link http://web3.ls.sp1.yahoo.com/readreviews?id=10069685&