Welcome to the forum. I have heard complaints and raves about all the Mass dealers so it is pretty much hit-or-miss. Your best bet is to go to more than one and price shop. Make sure they let you test drive it....if they give you some B.S. about how hot the car is tell them you are walking out right now if you can't get a test drive.
Don't settle for the first price they give you. Do not pay sticker. I don't care what B.S. they give you but no one has to pay sticker. Tell them you are ready to buy today. If you have a trade-in, tell them you are keeping it until you agree on a good price for the car...then throw the trade-in at them and demand Kelly-blue-book (settle for somewhere between "fair" and "good" value for your car).
If they give you any s***...just walk out. You are making a big purchase and should get the right price. If you are willing to wait a little while the price will only go down. You can tell them one of two things. "I don't have to buy this car today" or "I am buying A car today and you could be the sales guy who makes the deal". I don't think the first approach is going to work for the MS3 simply because the car is hot and they will sell them eventually...but if you can convince the sales guy he is about to make a quick sale then you might get the price you want.
Also, make sure you test drive other cars in the same market. The VW GTI, the Mini Cooper, Subaru WRX, etc. Know the competition and throw it in their faces. Nothing hurts them more than you telling them what you can get for another car...and if they say "but this is a Mazdaspeed" you say, that is great but I'm not paying for a name plate.
Oh, and don't smile...poker face. During the test drive if they tell you to punch it and gawk about how fast it is, say "yeah I guess...but the GTI felt just as fast". Don't let them know this is the car you want to buy today.
Check out some of the threads here and find out what people are paying so you know ahead of time what type of numbers you should expect to see. Only deal with total price numbers...not monthly payments. You can calculate that on your own ahead of time to make sure you can afford the car.