Individualised care of the Customer

We bought paint from the Sunninghill branch last Saturday to paint inside our house. I was extremely perdantic as I have had a previous experience that I was given the incorrect tint! i kept asking the gentleman the correct tint and as he was busy kept going from one customer to the other. I should have asked him to open the tins but he had already taped them up and had put small drop of the paint on the lid. so not being more dilligent took it! we started painting and the paint is darker than we asked for!!! I We are now sitting with 10 litres of the lighter shade that is far too dark and as I should have insisted the man to remove the lids I know I cannot bring it back but wanted to know if this paint can be remixed to 3 to 4 shades lighter.