Small companies are easy pickings. They tend to be more concerned about customer retention that corporates because each customer represents more of their turnover. They are therefore less likely to go to the courts to get their invoices paid. It is therefore far easier for corporates to bully SMEs than it is for them to bully other corporates. Add this to the standard policy of many corps of deliberately stretching out the payment cycles to improve their own cash flow, by getting an unauthorised interest free loan from their suppliers.
Ok - where is your spy cam? We are dealing with just such a situation in our "negotiations" with our big company client. Thanks for the laugh while we squeeze the $$$ waiting for our invoices to be paid!