How know a blonde

Blonde walks into a store and tells the salesman that she would like to buy the TV that is on sale for $200. The salesman says, "Sorry, we don't sell to blondes". She leaves, goes home, puts on a brown wig and sunglasses and goes back to the store and tells the salesman she wants to but the TV that is on sale for $200. He says, "Sorry, we don't sell to blondes." So again, she goes home, puts on a black wig, sunglasses and a hat and tries to buy the TV again. Again the salesman tells her
they don't sell to blondes. Finally she asks, "How do you know I'm a blonde?" The salesman replies "Because that's not a TV, its a microwave."