I have to agree with @Tut here. No one, not the auditors or even the government (at least for now) have the right of direct access to your accounting records. It’s a previlage granted by the owners.
However, as @Abanye said, it is a very good idea for more efficient reconciliation. Plus suppliers/customers can create their own non-financial documents (supplier quotes and sales orders) and attach files to them like invoices and receipts. This is not uncommon in many erps and accounting packages today.
This is a good suggestion if only you could select which supplier/customer account they can access.
Moreover, this method will inflate the number of global users to a point where administration and control might not be efficient.
Maybe if we have a restricted way to access and create restricted users from within each business and not have those appear in the global user list, this would make a lot more sense.
But the more I think of this the more it looks like it’s too complicated to maintain and may introduce vulnerabilities as @Tut hinted if I understood correctly.
This is why I think it’s better to create a separate portal for customers/suppliers that interfaces with manager from the backend and has it’s separate users.
I have already made something hacky using scheduled events and a cloud sharing service to but I would much prefer a native function.
Personally, I believe that regardless of how this gets implemented, customer/supplier/employee portals are the hottest trend as far as accounting packages go and will soon become the norm, if not a necessity.
I don’t see why this is not already in ideas.