The biggest problem for Point Of Sale system vendors are the traditional cash registers. Cash registers not only take a big part of the market, they also influence what shop owners expect from a POS terminal. Many shop owners switching from a cash register to a complete Point Of Sale simply want the same functionality and the ease of use of their old equipment.
I have done some POS implementations where I delivered exactly that: a POS system configured to emulate a cash register, with a few buttons on the sales screen to book sales on the various product groups, but without inventory control, reporting and all other features that make a POS system worth its money. The idea is to provide them the same way of working in a new environment to get the employees used to the new system. Once they now how to sell using the old-fashioned buttons I have them take an inventory so they can start selling using the barcodes on the items. Little by little they get deeper into the available features of the system, and the system becomes more valuable.
