Flag supplier as good or bad supplier

Hi

We have a requirement to stamp the suppliers as good or bad and the procurement officer should be warned/receive error if she tries to process a PO for the  bad supplier.

How can we achieve this?

I have tested Approve supplier list functionality ,it works fine except that it requires defining each item or each item category to be assigned to bad suppliers to prevent user to buy from them.

The issue here is that we have so many new categories or item created each day (we are a trading company, we buy and resell item,therefore new products ot product categories  created in the system every day),and it is not practical to use the Approve Supplier List functionality because of this.