A person files patent after they have disclosed info to public, and sold the item. But lie to patent attorneys. Also let previous patent pending on same invention expire. Can they be turned in for fraud?
Disclosure/sales by the applicant before the patent application was filed would be prior art. In the U.S. there is a quasi grace period of a year so the timing of the applicant selling a product embodying the claimed invention is relevant. An earlier application that went abandoned without being published might or might not be a factor in the validity of the patent.
If a patent is not yet granted there are ways to attempt to counter it at the USPTO. The AIA law introduced a new procedure called preissuance submission provision. During a period of the examination process a third party can, anonymously and for free, present documents that the examiner is required to take into consideration,
If already issued, there are procedures with the USPTO that can be used by third parties to invalidate patents by presenting documents that show there is relevant prior art. It would cost you tens of thousands of dollars at a minimum. In an infringement case the defendant can allege "fraud on the patent office" as a defense.
If the patent was fraudulently obtained and was used as part of increasing the value of a company in a potential investor's eyes that might be actual fraud but that is not within my expertise.