have an option of blocking a customer account. having to open the actual customer profile in order to re-activate it rather than with a simple "ok" while adding a new invoice. even creating a new "user access option"...
we process a large amount of invoices on a daily basis and it happens a lot for clerks to reactivate old customers with a simple "ok" click.
Guest
When you inactivate customers if you also change their status from Open to one which which is of type On Hold it wont let invoices be created for them. Create a new account status with a short description, eg "do NOT use".
As we can't rename account codes (why are Sage such a PITA over this?), we've started using "Lookup" accounts (customer accounts with the code that it ought to be showing the code that has to be used). Typically someone created an invoice against the lookup code, not the proper account code. We now put all those lookup codes on a hold status which says "Use the code displayed" when an invoice is attempted to be created against it.