There is plenty of business out there and the typical customer is not going to switch from someone they are happy with for a couple bucks. If I do a quality job, charge within the local market price range, and maintain a good rapport, I will continue to have a high retention rate.
At some point, I will take a summer vacation, have an injury, or have an equipment issue that the shop can't turn around fast enough. Maintaining a good relationship with local competitors gives me a stand-by network to tap into for all kinds of situations.
Plus, they call or stop by and warn me when they get stiffed or drop a client for reason so I don't waste time quoting the job, and I do the same for them.