Patience young grasshoppa, soon you will learn that there is no good reason on earth to pay anywhere near what the guy who bought it new paid.
Unknown rebuild means that stuff has been done to the engine and you don't know what, and don't know what parts went into it. For most people this is a big red flag.
ISIS is just like Megan or SSautoCrap, except that it's Enjuku's in house brand, so the customer service people are A) stateside so you can reach them, and B) speak English, and probably Spanish since I think they're near Miami.