Can they be sued for advertising patent pending? How?

Be aware that your competitor may have an unpublished patent application that may not appear in your search. For example, there can be a provisional application which would not be published.

A marking of "Patent Pending" or "Patent Applied For" on a product is notice to the world that there is a Patent Application, or a Provisional Application pending in the U.S. Patent Office or a PCT (international) Application currently pending designating the U.S. Since Patent Applications and PCT Applications are generally not published until 18 months after they are filed, and Provisional Applications are never published, it can be quite difficult to verify whether or not an Application is indeed pending. In addition, an inventor can request that the U.S. Patent Office not publish the Application at 18 months or until the Patent issues. You should keep track of when your competitor began marking his product as "Patent Pending". If and when a Patent issues, the competitor's filing dates will become known. If he marked his product as "Patent Pending" when nothing was in fact pending, the competitor has committed a "fraud on the Patent Office" and his Patent will be unenforceable. I hope that this helps.

Patent Pending means that at least a preliminary application has been submitted to the U.S. Patent and Trademark Office. If you are sure that the other company has not submitted an application, you can contact the USPTO and any state or federal agency that oversees the sale of their product.

The "patent pending" notice can be used starting with the filing of a provisional application - which lasts in secret for 12 months. Next comes a utility application - which can last in secret (if requested) up to the issuance of a patent - which could take 3, 4 or even 5 years. So - just because you could not find it - does not mean that the use of the terms is improper. However - if NO application exists - the use of "patent pending" is called false marking. Under the old patent law "anyone" could sue for false marking - and the award was $500 per item marked. Half went to the government and Half went to the litigant who filed the suit. The new patent law changed that - now only a person who has suffered "competitive injury" due to the false marking may file suit. The damages awarded are to compensate for the injury suffered - a hard burden to prove. These cases are now rarely filed. GOOD LUCK!