ambush invoice means: Modern American fraud to survive in a difficult economic environment. People between the ages of 25 and 38 most often use this method. This is the favorite tip of freelancers. Offer your services to people or companies that are perceived as having money. You are not hired by them. They ask for information and ideas, but you don’t have to give it. You then demand payment for all of the above. You can accuse smart people of lying to you if they refuse to pay. Send them an email with an invoice and a threat to spread falsehoods about them via Google if they don’t pay. Don’t laugh. It is widespread in America. (in Community Dictionary, added by Daniel Morris)