If I bought a set of golf clubs at a yard sale and later discovered they were forgeries of a popular brand, what recourse do I have to get my money back?

When you purchase items at a yard sale or any similar type of sale, you buy them with no guaranties and you buy them usually "as is". If you are on good terms with the person who sold them to you, go and see if you can give them back. Do not mention anything about the fraud. If this does not work, ask the person point blank if he or she knew these were forgeries/counterfeit and if this person fidgets, inform him or her that by selling these as genuine can be a criminal violation in your state for selling counterfeit products and as a violation of the unfair and deceptive practices act. You need to then talk to your local prosecutor's office (town or city or county prosecutor) and file a complaint and then also if that route does not work, sue the person in small claims court if the amount for which you bought it is less than the maximum cap in your state for a small claims action.