Somehow I do not think a PC merchant will ever be able to "instantly surround himself with guards with actual power of arrest and punishment and restitution," that would not be too realistic, would it? One can already hire, theoretically, PC guards but of course they have no more power than you but they might be able to relog faster. This is a prime reason to not put your wares out on a table, the ground or elsewhere. Make a book with a price list and put it out. when a suc--customer asks about an item you can show it to them in a trade window. The chance of loosing more than the price list in a crash will be much reduced. It might not look as nice but them's the breaks. It is better than losing your inventory to an opportunist.
Eventually an item bank will be implemented, I am not certain how they will use locks.