At no point did I suggest anybody board a POB and discover it sells contraband. If that was ever a thing, that's stupid because for a good while, Manhattan was a buy and sell point for Cardamine. Might still be if I could be bothered to check. So we can agree on that, but I don't see how it's relevant to this case. If it was relevant at some point, then I can see why such a ruling was made about boarding POBs - however, where this particular POB of which you speak was located, shouldn't be a factor. It's unreasonable to make a judgement about bases depending on what they buy or sell no matter where they are, or the whole of Manhattan is a drug den.
Besides that, I can see plenty of ways that your base could be proved to be hostile to Liberty. As I said, they don't need to prove ownership, all they need to prove is that the base is counterproductive to their aims. The two easiest ways for this to happen is somebody docking on it while being chased by the Forces of Liberty, or someone hostile to Liberty base-hugging it. Doesn't really matter whether its Unioners, Harmony or even a trader docking on it with a hold full of contraband while being chased by Forces of Liberty. If the current iteration of the Liberty Laws base licencing legislation applies to the independent worlds, then the base is automatically liable for a siege declaration whenever they want to write one, following notice to the base owners that they will need to pay a fee or be subject to the siege.
That's what I find so funny about the discussion you were having about who base-hugged against who. It really doesn't matter, if 5th, [LN] or anybody really were an active participant, they'd have all the ingame evidence and cassus belli they needed to lay down a siege notice and begin a siege.
But what are you worrying about? They haven't been bothered to do it so far.
