You don't know..

I went to buy a specific product from this shop, went home and used the product which i immediately noticed that something was wrong with this product. Took it back to the shop and the lady there changed it for me. Went home with another product used it and same thing noticed something is wrong. Took it back a second guy and this time the owner was there. He told me i do not know how to use the product and that they will not exchange it. After arguing with him for a while he eventually gave the money back and i left. I will not shop there again