Most car dealers would say that it's fine if you buy a car at another dealership, as long as it's made by a different manufacturer.

 When you go and buy the same brand they sell that might make them a little upset.  That happened recently in my house.  We have purchased three new vehicles from a particular dealership, we were very happy with the sales and the way we were treated, that's why we went back those three times.  When it came time to buy a fourth car we ended up going to a different dealership.  The reason for the change was simply based on the service department.  My wife bought a top of the line vehicle from the brand in question, she had a problem with the brakes squealing every time she backed up.  When we brought the car if for service at the dealership we purchased the car they just said the brakes were up to manufacturer specs and there was nothing they could do.  Three times we asked them to do something about it and nothing was done, my wife who thought this was unacceptable called the manufacturer and they asked her to meet the regional manager at a different dealership.  She did not make the meeting because of a huge snow storm we had.  The day after the storm the Service Manager of that dealership called and said bring the vehicle by and they will take care of it.  We dropped the car off they gave us a loaner and fixed the vehicle no questions asked, not a squeal out of the brakes at all, what a relief.  That kind of service earned that dealerships trust to us and when my wife decided she wanted to get a new vehicle the first place we went was to the dealership that went out of their way to help us out.  Let's hope that other dealerships take notice that it's one thing to have a great sales staff but it's also very important to have a great service department as well as support staff as well.