Ability to mark a thread as "Sold"

[90]

Pretty simple and I feel like doesn't need that much explanation but I feel as though once a sale is completed, there should be the option for the OP to mark it as "Sold" to prevent confusion and just for general organization.
Marking a thread as "Sold" would lock it and put a prefix on it rather than "Buying" or "Selling" it'd be replaced with "Sold"

Yeah that's all. Let me know what you guys think of this idea of if you have anything that could be added to it to make it better, thanks. 

EDIT: There could also be a function that sends an alert to those who replied to the thread or made an offer and let them know that the handle or item has been sold just so they are aware.

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