The time to enter into a commission contract is before you disclose the buyer, investor, etc. This is now a question of whether you have leverage, because it may be too late to protect yourself. I specialize in these types of legal issues, and I always have difficult time explaining to clients that they need to protect themselves beforehand. It's a careful balance, trying to get a deal done and protecting your fee.
I'm not sure where you get the 90 day right to rescind a sale of a business. Your sale is governed by a contract and any advertising or other representations made by the seller. Can you provide more info?
Bankruptcy is a highly technical area of the law, and it's not recommended that you represent yourself. The bankruptcy trustee's job is to "marshal the assets" of the debtor in bankruptcy, which may include payment to you. Find an experienced bankruptcy attorney.
In some states, such as AZ, if you pay another person's property tax for so many years, you have a right to the property after so many years. If the property owner comes and pays the tax bill at the last minute, the tax payer receives his or her money back plus statutory interest. Depending on the economy, this could be a good return on your money.
Call the tax assessor in the area and inquire.