1.) allow players with learned recipes to become "crafters for hire" (checkbox option somewhere)
2.) allow players to check what items another player can craft (provided they choose to craft for others, so anyone that knows a recipe cant get bothered by other players)
3.) allow a player to then express interest in having the other player to craft said item

[up until now, nothing is binding, just an informal interest in crafting an item]

4.) the crafter then sets the terms for the trade, which are broken into an pre-craft (up front cost) and a post-craft section (payment for final item)
5.) the pre-craft section is autopopulated with the required materials/CE/crowns, and the crafter can choose to deselect any or all of those. if the item requires other items be crafted first (lower star versins), and the requestor cannot provide an unbound one, then the raw materials/costs for those earlier weapons can be tacked on as well. any weapons that need to be leveled the crafter is agreeing to level on their own (which they can factor into their post-craft cost)
6.) the post-craft section can be whatever. a crown tip, nothing, materials (maybe the requester is asked to try and accumulate some of the required materials before the final delivery, but the player can start crafting it now)
7.) the final term is a number of days the crafter has to fulfill the request
8.) the person requesting and the crafter then sign off on the terms. this is saved and is now a binding contract. pre-craft materials are then provided to the crafter, if the requestor doesnt have them it cant be signed (but maybe can be saved as a pending contract, that can be signed when ready)
9.) the crafter then has X number of days to craft the item (and perhaps these agreements can be done without the two players being online at the same time. there could be a text field for the users to add messages when negotiating the contract.
10.) the crafter then provides the item, and the requestor completes the payments from the post-craft section
11.) if all terms are met, hooray! (crafter/craftee is given a good rating)
12.) if not, the players whose conditions were not satisfied can choose to extend the contract a few more days, and possibly a "late payment" or some sort of penalty is tacked onto the contract for the person that fails to uphold their end of the bargain
13.) if they choose to not extend the contract, then penalties are enforced (items reset back to pre-contract status, if the mats/crowns/CE can't be taken from one player to refund the other, then.. something happens so the player due the refund gets what they lost)
14.) players who fail to meet contract terms are given a bad crafter/craftee rating, other player is not rated for this transaction.
15.) players who repeatedly fail to meet contracts will not be allowed to enter contracts with other players for a period of time

also, crafters can save a contract for each recipe they know, so they can offer the same initial agreement each time. if the player offers a pre-made contract, the craftee can view that before expressing interest,

this way players cant rip each other off, change terms of their verbal agreements, admins have a transaction log of who agreed to what, and you can tell who is a reliable crafter/craftee.

i just came up with this off the top of my head, and the penalty/refund part would probably be a bit tricky. there are probably other holes in it too, and its maybe not as straightforward as I'd like it to be. but it could work.. maybe.