I don't know why, but I LOVE retailing!
I think a lot of clients appreciate hearing the truth, and in the end they just want to know that someone cares and is willing to listen and help. When I retail I talk to them like I would talk to a friend. I make jokes, I refer to my own use of products, I try my best to make them feel like we're just two girls having a chat about product. There's nothing worse that being sold something with what you know is a well worn spiel or dialogue, it feels forced and fake.
Retailing is a long game. You put in the work and create the trust now - and they'll come back.
In terms of particular products not selling, I would chat to your rep about this as they might have some ideas. Having worked with dozens of brands over the years there are always a few products here and there that are a tough sell, but this is part of knowing your demographic, and knowing what will move and what doesn't. You don't have to sell every product from a skin care or makeup line, cherry pick the ones you know move and sell the sh*t out of them!