I think they are offering some assurance too because they are acting as a middleman, well there are some trusted escrows in these forum and not all are scams and in my opinion I think some reputable escrows here will accept payments even if it's not that high than scam people out and destroy their trust.
But because this is an international organization and almost all of us here are hiding at the back of our computer it would be hard to find someone that you trust unless you know him for a long time that's why escrow are created and yes it's better to pay high in the reputable ones than pay on someone claiming that they are escrows but in the end scam people out.