advantages of a long back
I know that long back does equal weak, but it also equals the potential for more flexibility and correctly worked, it can mean a "softer" ride than the pounding of a very short backed horse. The good thing about Flame is that his whithers tie into his back WELL BACk, so if you look at him, his back isn't as long as you think. A lot of that visual length is actually his neck which starts way back behind the shoulder . This is good a long neck balances out a long back. If he had a short neck, then you would be in trouble. He has a kind eye and a relaxed face, unlike many Arabs who seem tense. I like his large , outwardly pointed ears. How are the feet? Large? This is important. His shoulder slope is decent. Hip is a bit weak, but he is just undermuscled right now.
I would watch how his owner rides him and this will tell you a lot. For example, if she rides him with his head stargazing you will see why his lower neck muscles are developed and the upper ones underdeveloped.
For the price you are talking, if the horse has a nice personality and good feet, I would take him and make him your best friend.