In OpenCart Marketplace Product Quote System, the admin can set the minimum purchase quantity for the products which are available for quotation. The value mentioned in the Product Min Quantity will be applied to all the vendor products.
But, if the admin sets the option ‘Seller can add minimum quantity‘ as Enabled. Then, the value mentioned by each vendor will be applied. So, whatever the value set by the vendor, greater or lower (in comparison to admin) will not matter.