What is a consignment house? Its a reverse Auction House. Basically, the potential buyer goes to the proper machine (Shard or Item) and places a request for a specific item, $$, and (optional) ingredients. A crafter walks up, and attempts to craft the consignment.
On success, crafter gains the ingredients and the money. The completed item gets sent to the Consigner.
The Consigner can set a % threshhold that limits any crafter from attempting to use supplied ingredients. (Any crafter can still try, but if they don't have the %, they must supply their own ingredients, though still get the ingredients on completion).
The Consignment house works $$ wise exactly like an Auction house. (Posting fee, 30% deduction on delivered funds).
Basically there would be two separate consignment houses. Shards and Items.