We do that already via an online sms website...reminders, let them know their car is ready, specials etc.Yes,The dealership i go to,sends msg's as well as feedback ratings after service. Something to consider.
LOL - the feedback ratings - folks most certainly come back to tell you if they are not happy - the "ever since" factor
And, there are those others who don't say a word and never come back - and "slag" you to 100 friends as well.
That; of course; is the majority of folks in life and in every industry - non-confrontational....vote with their feet.
Every now and again you get a nice recommendation and/or a bottle of wine from someone.