the case is, is buying trust allowed? i think it is not, right? What if 2 accounts fake their deal and used a escrow in depth 2 to get a trusted positive feedback? is it allowed?
It is allowed, however a competent escrow will avoid giving trust to two users who they generally do not deem trustworthy after just one or two transactions. If they are too liberal in giving out positive trust after acting as escrow, someone will probably say something and they will probably be removed from the DefaultTrust network