Whilst I can completely understand this must be very frustrating, there isn't actually anything we do in this situation, the specific formatting is how the system works. There are several guides on the site and on signs around the server which explain exactly how to set up shops, and you must have accidentally done it incorrectly.
Whilst morally it isn't really nice to bankrupt you by selling to you at an extremely inflated price, this is a mistake on your part and so the user who did so was doing nothing wrong going by the actual rules.
Moving on from this I would suggest you double check every shop you make in the future, and learn from your mistake. If you are having money issues in regards to keeping your plots/town membership I suggest that you try selling off some of your stuff.