Mercator

Market share

Customers and Custom

Be careful to distinguish between customers and custom. Many companies describe their business in terms of market share. Market share, however, is a measure of custom rather than customers: a business that has 20% of the market may get business from 30% of customers in that market but because not all the customers buy the same brand every time, it averages out at 20%.

This is why promotions are not good at winning customers in any permanent sense: all they really do is let you bring the tide in towards your brand when you are promoting but leave you watching it go out to your competitors when their promotion starts.
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