pushing aside all of the other reasons not to get this gelding, I would not buy him.
He appears to be calf kneed, butt high, and long backed just in these photos. I also see a collar on him, which means that he has atleast some history of wind sucking or cribbing- both nasty habits that are hard to correct.
I will add a few that I can see... He has an undesireable LS placement, and long loin, I do not find he has an ideal neck nor does he carry the condition which makes me think that any of these things are an illusion from poor photo choices.
To explain things better so it doesn't seem like everyone just wants to make you miserable.... Being downhill (butt high), means his balance is naturally on the forehand, which is opposite to what we want to see in a riding horse as it inhibits the horse's ability to round the back and lift it in order to move correctly, the LS placement is important because it is the "hinge" by which the hindquarter swings, the further forward that joint the more power the horse has and the more ability to change gears, his long loin weakens it all a bit more as the loin is a major support for the back.
Being calf-kneed (or back at the knee) is a moderate to major leg fault, depending on the rest of the horse's conformation, the purpose the horse has, and the severity of the fault. It will cause additional wear and tear to his joints, sometimes permanent damage such as bone chips and tendon tears if he is worked incorrectly over any real period of time.
Add the cribbing or windsucking... And you have a horse that will take a lot of knowledge and experience, time and money to get fit, keep fit, and maintain the health of.
Overall I find he looks rather, frumpy, for lack of better description... I would pass him over without a second thought.