Give an option to block certain customers. For example make sure that sales can't enter an order for a customer that didn't pay his bills. Now you can put a customer on inactive but if you create an inactive customer as a new contact the system allows it (even if you uncheck the box for allowing duplicate contacts) and the order can be entered anyway without sales knowing that the customer is blocked.
Raja Selarka commented
This features is badly needed in my business. It is hard to keep a track on sales people and monitor each and every transaction. We have more than 800 customers and we have more than 250 deliveries per day. It is impossible to track and block customers who do not make payment on time manually. There must be a auto system which stop my sales people or tele caller to enter new orders from such customer but at the same time, these customer should not be disappear from the system the way it has happened when you inactive clients in existing features. This is even more scary as you do not see them on system so people do not follow up for the payment.
This is an essential function when dealing with customers who do not pay - please add some way to flag/block customers who do not pay their bills.