It took me several bike shops to get a shifting issue on my bike fixed. You might try another shop. I also ended up emailing the manufacturer and they put me in touch with a different shop to work with as I was not happy with the place I bought the bike.
As far as putting on mountain bike tires on your Sport, be sure that there is enough room for the width of the tire. I put knobby 1.7 tires on my Cannondale hybrid, that normally wears 1.5. So, the size wasn't much bigger. However, I noticed a couple of days ago that the inside of the fork has paint rubbed off of it, all the way through the paint. Even though it looks like the tire has clearance, riding clearly has causes the tire to rub the fork at times.
Because of this I think that I have to go back to narrower tires.
Trek Madone 4.7 WSD
Cannondale Quick4
1969 Schwinn Collegiate, original owner
Terry Classic
Richard Feynman: “The first principle is that you must not fool yourself and you are the easiest person to fool.”