I don't know how much you know about specific terms, so bear with me if you already know...You know how your tire gets put on right? You take off the lugs, and there are 5 "studs" that hold the tire in place. These studs are permanently fixed (pressed) into a "hub." This hub is bolted to a big part called a "knuckle."
If there is any reason to believe that the bearing is shot - you'll need to un-bolt the hub from the knuckle and replace the entire hub (~$253/hub - I just looked it up). Most all part stores, and dealers would not sell just the bearing. You don't want to ever take apart a sealed bearing. The bearing itself is ~$9.00, and unless you have the appropriate tool to press out the bearing from the hub - there is no need to remove the bearing. If you're actually going that far to press out the bearing - for $9.00 you most likely would be replacing it. But again, most dealerships & part stores sell the hub with this bearing pressed into it. You following so far?
With the window rolled down you MIGHT hear some clicking/ticking sounds, esp while turning. The wheel MIGHT also move if you push on the top of the tire itself. If you were to grab the top of the tire itself and push and pull it towards and away from your self, it MIGHT be moving in such a way that a mechanic would know its bad for sure.
Also, consider going to another place to get another opinion. Try a smaller repair shop not a chain repair shop - if you think about it they really have to compete out here for business aganist all the dealerships. A smaller repair shop might tell you a little more, be more honest, and save you some money.
If you want to go to a different dealership try getting the guy who is actually looking at your car to talk to you. Have him show you what he is seeing. That's always good to know for the future.