This is what Scott Wozniak, who works with Chik-fil-a, calls "raving customers". The idea is that loyal customers are great, but raving customers are what you need.  A loyal customer will come back, a raving customer will tell everyone how great Bentleys are.

Interestingly enough, I was at a meeting with Scott and he related a story that Subway, about 2010, approached him to help implement this concept.  Scott was nervous about divulging Chik-fil-a strategy.  He asked the CEO if and what he could give to Subway.  The CEO told them to give them everything, up to an including the operations manuals. The CEO also told Scott not to worry because Subway would not implement any of it.  This was 15 years ago, and Subway has done nothing.