I paid for my bike and accessories so they've already milked me for quite a bit. At this point it is primarily customer service to keep future business. So because I like them I'll go in and buy new intertubes, gloves, or anything else that might wear down. If I'm happy with their tune ups I'll end up taking it back to them after my year of freebies is over, etc. I'll also recommend them to others and what not.
This type of customer service seems to be lacking from buisnesses more and more so I'm just happy to see it alive and well.