I received the following PM from SourceBOT:

A post that you created has been removed:

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Post ID: I purchased 1x TF2: Mann Co. Supply Crate Key from him via......
Thread: Aard's reputation thread
Reason: Your trade partner did not leave a counter-rep for this transaction. Contact them, then post a rep again.
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He actually did leave counter-rep: IQAndreas' +REP Repository

However, upon further inspection of the FAQ, I now see why the +REP I left was "invalid".

I have made a Rep Thread now, and was wondering, when the SoruceBOT deletes posts, does it permanently delete them, or soft delete them? I will send Aard a message and ask him to reply to my SourceOP Rep thread, and after he has done so, is it possible to recover the post I wrote in his Rep thread? I could re-write it, but it was over a week ago, and I can't remember the exact amounts, nor exactly what made the transaction with him stick out above others or how I worded it.