Not allowed to test a product

I was at New World Menlyn Park and was looking at the digital pianos they have in stock, being a highly prospective customer. I sat down to play one in order to test how it sounded and felt, because that's one of the very main things which sell a product to me. After a minute or two did I only notice that I had to ask for assistance in order to touch the product, and promptly saw a staff member about that. I kindly asked for permission to play it and told them that I am looking at pianos for home use and that I'm a very likely buyer of one of their products, and after a while they said it's fine that I may play. I returned and sat down on the bench, starting to recite my most favorite of songs on that piano - a Yamaha Arius digital keyboard. I was happy until the security guard told me that I am not allowed to play or even touch it, to which I responded that I have permission. He just shook his head and told me that he's not going to allow me to play any further. I am a very introverted and shy person in real life and I loathe going to the mall where there are so many people, but I never thought I could throw such a fit in the middle of a busy store. I am deeply disappointed.