car shakes at high speeds after tire rotation

OK, so I took my Saturn LS200 to a mechanic to get a tuneup (oil change, radiator flush, etc.), including a tire rotation. I had no problems before that, except the car would slightly vibrate at around 66 MPH but not at all under or over that speed. But now, when it hits 65, it starts vibrating, and gets worse at higher speeds. I tried putting air in the tires, no help. Did these guys not balance the tires after rotation? I want to go back and ask them to fix it free (shouldn't they have tested it on the lift for vibration before anyway), but I don't want to get scammed. Advice?

before they did that was it kinda shaking in your seat and not in the steering wheel?. unless you ask them to balance your tires they wont. it cost extra. sounds to me that the tires that were on the back were not balanced very well. take it somewhere and have them balance all of them. ask them when they balance them to look for any broken belts in the tires. that could cause it also. hope that helps

Thanks. I figured they would rotate and balance, but guess not. I took my car back and they rotated the tires back the way they were for free and told me the rear tires weren't balanced right and the tread was uneven. That took care of the shaking for now, so I will probably just get new tires at some point and make sure the place aligns/balances them as part of the installation :-P