No-one is banned from oof unless there is a very good or repetitive reason for it. It does not matter how many post points oofers have, it does not mean that they are experts or know all there is to know. The post points indicate how regularly they visit the site and post a comment. All oofers do is try their best to advise from their own experiences. Some, such as Darth-Loo-Knee and his cronies really do know their stuff and their advice can be trusted. Whether or not any advice is taken is very much the decision of the asker. Do not take this out of context. Point is this, some very basic precautions should have been made before you parted with any cash.
Never buy an car unless you either know what you are looking for and have the necessary knowledge to inspect it thoroughly. Always take someone with you that is knowledgable and who can then also act as a witness to any statements that are made at the time of sale. Make notes and take pics, they all come in handy at some point.
As for you problem, all you can do now is to start from scratch and inspect and test everything in order logical sequence. Do not jump straight to the head gasket which always seems to get the blame, because there are many other things that it could be that will not be anything like as expensive to put right.
Patience is a virtue, posses it when you can - as the saying goes!
As before - try to get in touch with markey mark and see what he has to say. You may get a surprise.
GudLuk