To fight grieving:

SE just has to make the issues mats temporary until the leve is completed.

I would assume the model will look something like this.

1: Player puts in a buy/sell order along with his own mats.

2: Player X accepts the craft bid offer thus locking out others from attempting the craft until the buy/sell order is completed or failed.

3: A timer is started which regulates how long the buy/sell order can be exclusively locked to Player X. If the timer expires before player X completes the buy/sell order. The leve is canceled and becomes open for others to accept.

4: Player X is issued temporary craft items (which either used only for that buy/sell order or destroyed post leve timer expiration)

5: player X crafts the buy/sell order and is awarded upon turn in if successful.