Why do you think the optician reacted this way?

I went to the optician today to ask for contacts lenses prices because I have never worn them before and I have been considering. They explained the prices to me of different brands and they listed them out on a piece of paper. When they were done I asked if I could keep the piece of paper for future reference when considering what contacts I wanted to buy so I could think it over, but the lady quickly snapped and said "No, you cant!" and she quickly threw the paper away. I thought it was so strange and random, its not like my request was unreasonably? Could they be hiding something about their products, or am I overreacting?