Everyone hates duplicate customer records. It makes customer service so challenging. It would be AWESOME to have some tools to prevent them rather than just having to deal with them using the Professional Service Tools after the fact. Here's my idea:
When you get ready to add a customer, rather than immediately provisioning the next live customer number and writing to the GP tables, it would be held in a temporary table until hitting the "Save" button.
Then, some data validation (Perhaps these would be settings or options for what fields you want to valide) could be checked. For instance, is there another customer with that email, phone, address, name. If the database finds some potential matches, they could show you the data in a grid and prompt you to use an existing customer instead.