Within Bonfire, you can edit BidTables to allow vendors to choose if they wish to Bid or No Bid on a given line item. This option is turned on by default.
Once a BidTable has been made, you can choose to turn this option off by clicking the BidTables section and then Actions -> Edit next to the BidTable you'd like to edit:
You will then see the BidTable Editor. Once there, you can select Edit BidTable from the Actions menu.
Once you have selected Edit BidTable, you will see the Edit BidTable popup, as shown below. At this screen, you can choose to turn off the No Bid option.
Once you click Save, the BidTable will then require vendors to fill out the entire BidTable and provide a bid for every single item you've listed.