When we do a new sale, we want it to be put automatically the last price negotiated with that customer. There is a module or a way to getthe previous invoices to search if the product has already been sold to that customer and at what price? An then, insert in new invoice that product with the last customer price and not the default product price.
e.g.
We have a glass in the store for 5€. Last month, we acorded with John to sell him at 4.80€. So in next John's sales, when we put glasses in a John invoice, we want do it for 4.80€ instead 5€.