I would like to know the average percentage of shoppers who, after
visiting a supermarket for the first couple of times, become a regular
customer for the store. I would call it supermarket visitor to
customer conversion rate. (ps: This question is for brick-mortar
supermarkets in the United States, not online stores or other
countries.)

Here are some background: a typical supermarket has about 30% annual
customer defection rate. Which means 30 percent of the customers who
shop at the supermarket this year will not be shopping at the same
supermarket next year. For a supermarket to stay healthy, it needs to
get new customers and convert them to regular customers. What I mean
by regular customers are customers who would shop at the store
regularly for a year or longer.

Marketing efforts such as tv advertising and weekly circulars will
attract shoppers to the store. However, not all first time shoppers
will become regular shoppers. What I would like to know is the typical 
conversion rate: the percentage of customers who do become regular
customers.