The cost of lighting a cigarette

I was walking in an open mexican marketplace tianguis, I saw a very poor woman selling spare cigarettes. I wanted a smoke, so I reached into my pockets to find spare change. Instead, I found a pack, but no lighter. So I deliberated how much lighting my cigarette was worth, and I concluded it was three pesos. I handed the money to the woman and lighted my cigarette, but she gave me the money back saying it was not necessary.