You are asking a legal question that only an attorney in your jurisdiction would be able to answer. An EULA is a contract between you and the author of the software you are licensing, and your use of the software is basically your agreement to uphold the contract. Most EULA prohibit re-sell, although I have not read Flight Factor's EULA as I do not own the software. Some jurisdictions (in Europe, for example) refuse to enforce these provisions. In others, however, they are a valid binding contract and you would be in the wrong to re-sell the software. My personal feeling is that within the flight simulator community you are playing with fire. Just chalk up your dissatisfaction with the software as a loss and move on.