Pretty much the same thing happened to me. I was all set to buy a very large TV. A fairly pricey item. They salesman tried to sell me cables. I said I had some. He tried to sell me a sound system. I said no. He tried to sell me something else. I said, "Look, here's my credit card, there's the TV. I am buying the TV. Not one other thing. If you try to sell me anything else, I'm walking out."
He said, "Okay. Okay. I get it. Ummmmmmm, would you like to buy a three year warranty with that?"
I haven't been back since.