It strikes me the BO does not know how to deal with "thresholding" attacks, which might not be surprising as it's usually only reserved for forums that hit very close to the truth.
As per my previous statement, a "threshold" attack tries to find the threshold (hence the name) of when a shill post is largely indistinguishable from a normal post.
Naturally, spotting thresholding attacks is hard. But you must also be extremely careful not to allow the other side of it's edge, which is to make legitimate posts seem shill-ish.
If you delete an innocent's post, or you fail to spot the threshold attack, it has succeeded - because deleting innocent's posts will alienate them from the board which will succeed in driving them away from the forum.
It's actually better to err on the side of caution, and instead, either watch to see how a threshold attack develops (remember, it cannot remain legitimate for long), and if anything, apply pressure in the form of questions.
Short-term shills will lack sufficient local knowledge to validate themselves (but can be easily confused with newfags). The difference between shills and newfags is shills will always try to exploit hostility and DARVO, where-as newfags tend to concede or admit errors.
Long-term shills will be able to pass typical background queries, but their threads or writings will still contain fundamental flaws: the tip-off is when they REFUSE TO CORRECT THE FLAWS.
Accidental errors often bring concession and admission of error followed by a correction and no further continuance. Intentional errors are either very recluctantly 'corrected', if at all, and the behaviour remains the same in future (like a repeat offender).
Thresholding attacks only counter is observation, questioning and due diligence with expected psychological profiling of typical reactions.
Do not 'kneejerk react' because you might cause collateral, and resistant innocents (who are offended at bad adminship) are nearly indistinguishable from resistant shills (who are opposed to adminship period).
Threshold test: If someone was to enter the room and ask me to prove this was likely a thresholding attack, would I be able to prove it to them?
If yes: it's a threshold attack.
If doubtful: more time observing required.
If no: it's legitimate.