My tandem-mate and I took our "bicycle made for two" here for a standard tune-up since we hadn't had one since we bought the bike.
The staff (owner maybe?) was very friendly and knowledgeable about our bike: an example, he told us that Shimano, the maker of our tandem, was notorious for poor gears. Our bike did, in fact, have a hard time shifting gears. But when we picked it back up he fixed them!
The Golden Spoke is a great place for a cheap tune-up (only $40!). The service will take a couple of days, but it is well worth the wait!