What should the designer say when he sees the customer that the decoration company has friends?

The first thing is not to worry too much. Usually customers say this because there is no trust between them. So, you should ask the company that asks customers why they don't use friends. Only in this way can we understand each other's thoughts and identify each other's real motives and needs. Then you can communicate with each other according to their answers. This will make it easier for customers to trust you.