Actually, I think this is common in the IT Industry too, especially with System Integrators etc.
Think of SAP, Oracle and Microsoft. They will turn up at big trade shows and have sales teams showing enterprise solutions etc. Try and buy an Oracle ERP solution it probably would come from a reseller - i.e Accenture or Capgemini etc.
I know with the likes of a Microsoft you can meet their salesman and they'll then advise you on a good / preferred partner - i.e Software Integration ltd to act as a commercial reseller and implementer of their solution.
Thing to remember is the reseller also has in their portfolio Oracle and SAP not just Microsoft.
Ok more complex than a drink but principle is the same.