demon customer

The age of "the customer is always right" is over for some retailers where big box store Best Buy for example, refers to a "demon customer" as one who ties up a salesclerk but never buys anything. Or who buys only during big sales.  Or who does research online and comes into the store demanding the same item. Or one who files for a rebate, then returns the item.

NetLingo Classification: Online Jargon