There seems to be some trend developing in regards to trade and war in general.
As neutrals in the war, it may be helpful for participants to understand our views about trade in general (and by neutral I do mean without alts on one side or another ).
If you are in the war and know you have a blockade/siege at your city, it would be extremely poor form and bad etiquette to buy from the public market and knowingly expose an innocent 3rd party's vans to seizure. Trying to pass this off as the fault of the person doing the blockading does not pass muster.
The innocent 3rd party trader puts up a sale on the market expecting nothing more than a business deal. If you order their vans into a war zone, it is your act that triggers the risk to the seller, the person doing the blockading may or may not have a reason to be blockading you, but that is of no matter to the trader. The blockading party did not order the vans.
From a personal standpoint, if i lost vans to blockade where the buyer knew the blockade was in place, but was so desperate they risked a market buy, I might well be tempted to join in the siege and recoup my vans cost and the time and effort to rebuild via more punitive means.
If you are under siege and blockade, look to your alliance and confeds for help and leave the market out of it....
.. simple common sense really.