Of course that's where a good manufacturer to distributor relationship is important - Communicating with the manufacturer why you're not looking after the customer currently should allow you to work out an agreement. Also - getting a
credit card from questionable accounts is always a great idea.
As a rule - I don't think I would everr shut anybody down because of money (I've never let an account get that far behind), but I will always require payment of old invoices before selling new parts or supplies.
As far as the manufacturer / distributor support debate - I think both are equally important, but perhaps a little bit more importance should be put on the distributor. The dist. is the person who is selling, installing and maintaining this equipment at a hands on level - They can take a poorly manufactured un-supported piece of equipment and make it great. But they can also take a high quality piece of equipment with full manufacturer support and turn it into garbage - I've seen both. The manufacturer has a responsibility to manufacture to the best of it's ability, and give top notch support to the distributor AND to the customer when necessary. I feel the distributor should always be the first phone call from the customer because they are most familiar with the little details of the installation, and system history.