This is a very cool business. California Typewriter is also good. But prefer BTC. Both have been around since the day when every UCB office had an IBM Selectric. BTC used to be Channing Way, two blocks from campus and had the service contract. Now they are on University, or low rent retail strip. California has stayed on Bancroft where I first used them back in graduate school. I bought an electric Facit portable from them when I could afford it after grad school when I couldn't.
A couple of years ago I bought a 1940s Royal portable on line and it had problems. The guys at Berkeley Typewriter fixed it in a couple days. I was surprized how many people still use typewriters. Their benches were full and the fixed machines with tags for pick lined their shelves and floor.