Going to be honest, you should just try to get your money back from your neighbor. There is nothing wrong with asking for a refund due to the coin being a very bad Chinese counterfeit. Since they are your neighbor, a refund is certainly an option. Get that money back, you don't need to lose it to learn a lesson!
@MisterT The Seated Half series is pretty fun. The links that Heymikep posted are the ones I've been using for a long time. It is very helpful. For some of the years, various mintmark sizes were used, but not every year. For example, the 1870-CC and 1872-CC only use the large CC mintmark. It is also helpful when deciphering years on worn coins occasionally.
@MisterT, you are incorrect. Liberty Seated Half Dollars came with different sized mintmarks. Also, besides the fact that the mintmark is different than what you saw, what other evidence do you have? Surfaces look correct, does not look cast, everything looks normal to me. It is an honestly circulated San Fran Half.