Your recourse may be to sue your agent for malpractice. The agent has a duty to obtain the highest and best price for the property. It is extremely rare that an agent would not start with a price that is above market, because the agent's commission is tied to the sales price. There are only two rationales that I can think of for setting a below market price: (1) failure to correctly perform a comparable market survey (CMS); (2) conspiracy with the buyer to obtain the property at a lower than market price.
If #1, then you have a claim for malpractice. If #2, that would be a fraud, and a criminal one at that (false pretenses). You could refuse to sell (rescind the contract), regardless of whether #1 or #2 is the reason for the low price -- because for #1, you made a material mistake going to the basis of the contract, and the buyer knew or reasonably should have known of your mistake. For #2, the contract would be void as illegal.
Ultimately, if the buyer decides to force arbitration
, you could find yourself in a pretty expensive legal battle -- which is why I say you may be able to sue your agent for malpractice, and force the agent to pay the difference between what you received and what you should have received from the sale.
You may want to tell your agent that you are going to refuse to transfer title
and sue for malpractice unless the buyer either agrees to a higher price or to cancel the contract -- or, the agent can agree to reduce the sales commission to make up for the lost revenue (assuming that's sufficient to make up the difference).
It's certainly an ugly mess, but you do have several possible legal recourses. Hopefully, you can settle the matter without heading to court.
Please let me know if I can be of further assistance.