It's possible that when they "checked the bearings" they just jacked up the trailer and spun the wheel to see if it turned and didn't make any noise. Or they could have just looked at the outside of the wheel and since the wheel hadn't fallen off the bearings are good. :) Very hard to say.
Having the bearings and brakes checked is probably a good idea since you have no idea how many, and what kind of miles are on it. The price for the service sounds pretty good IMO, but you might check to see what the parts would cost if he has to replace brake shoes or bearings. I just did half of the wheels on my triple axle toyhauler and it's a pain, so having it done for a decent price is worth it in my book.