This is common? To me that looks like the member had “a bad day” or a temporary lapse of judgement more than it being an account created with the intention of causing mischief after establishing some trust.
In my experience most accounts that are created for the purpose of mischief don’t invest in the forum and either reveal their intent immediately or after a very few posts at most.
Not that a good member can’t turn bad, only that from what I’ve seen it’s more rare than a bad member turning good.
A lot depends on your Moderator team and how well member Flags are working for you. Where I am a moderator we have set the edit window for a few hours. There is enough overlap so that if a moderator sees a post before it later gets edited, a staff member that has “later hours” will see the post after it was edited and Flag it. By the time a post is old enough so that an edit might go unnoticed it has already become uneditable.
Maybe if instead of shortening the edit time window, you made getting to Trust Level 1 a bit more difficult it would help?
D’oh! I saw the number of posts, but didn’t spot the time frame. That makes it look more like “fluff” posted expressly to gain Trust Level (not that it does, but it seems some think that it does)