In the Marketplace where a product has more than one vendor listed I suggest that one of the vendors is nominated as the primary vendor to be contacted for product support.  This would ensure that a customers concerns would get addressed by the vendor most familiar with and has the most knowledge of the product.  

This could easily be addressed at the time of uploading the product for testing.  An additional field requesting the nominated vendor for product support could be added.  This would remove the need to delete Marketplace items that have more than one vendor listed simply because one of the vendors does not log in frequently enough to provide this service.

My Renderosity Store
Virtual Furnishing
My Portfolio