under GA real estate purchase and sale laws what is a buyer's right to cancel sale, buyer found black mold during renovation

This is definitely not an area of law that you should in any way attempt to undertake on your own. There are circumstances in Georgia law where you may be able to rescind a purchase (it is technically NOT a cancellation of the contract) but there are specific steps needed and the process may not provide remedies appropriate to your situation and you may not be entitle to recover the costs of your damages.

Also there are many types of mold, many of which are not harmful to humans in most circumstances. There will need to be testing and remediation may be possible, which may be most cost effective that a legal action to attempt to rescind.

Please consutl legal counsel in your area promptly to determine what rights and remedies are available.