There is nothing really free in the world

Yesterday I went to Big C Wongsawang.
While I was walking out, a man at a stall in front of enter gate called me “Do you have a receipt 100 baht up, you can get free gift set here”.
I read the sign next to him that was written that “the receipt 100 baht of shopping at Big C can exchange a free gift here”.
I’m quite interested in so I decided to walk to him and gave him my receipt. He showed me a set of knife that included 3 pieces and 3 style of knife. And then he started talking about the product story, the quality of product, where is it come from, how shape it is and then he showed me testing by cutting my receipt. While he was talking he often asked me what I am think about, is it good? I nodded and said “yes it is a very good product”.
He talked very long. I can’t remember what he says but the last sentence. “Today, special for you only 199 baht” he said. I was stunned for a while. Then I said “What? 199 baht it’s free, isn’t?” and I pointed to the sign.

I hope he will say sorry but no. he said “There is nothing really free in the world especially a good thing. It’s very cheap only 199 baht for 3 in one set. you just say it’s good.”

His word made me very angry so I walked out immediately. I was in a bad temper all day. Stupid me I believe it’s free.