1) There is no general right to a refund in this sort of transaction, so as a general matter, returns or refunds only have to be provided if the seller agreed to do so, except as set out in 3), below.2) More specifically, with only a few exceptions, if someone buys something "as is," he or she is taking the risk that it will not work, is broken, etc.3) The only time that a private seller in an as is transction typically would have to refund money is if a) the item sold was not the item advertised or agreed to be sold; or (b) the seller either misrepresented important information or withheld important information in such a fashion as to deceive the average reasonable buyer. Otherwise, if there was full disclosure of everything the seller knew, the buyer would not typicaly have the right to a refund.If this person is threatening you, you can contact the police.