The employees are key. A good selection of parts helps, too. I pretty much insist on an excellent repair/parts department staffed by people who know what they're doing and won't try to sell me something I don't want or need. Also, it's good to have people who don't get too snobby about bikes. If a person shows up at the service desk with a $400 hybrid and a flat tire they don't know how to fix, they should be treated the same as someone who rolls in on a $4000 road bike.