Must I hire a broker to oversee my transactions? What if I trust my transaction partner?

If you know your transaction partner, then there is no need for an escrow. Both partner can exchange goods, products or funds without having a third party over see their transactions.

An Escrow is a service which provides you with a means of protection in the handling of funds and/or documents. Escrow enables the Buyer and Seller to transact business with each other through a neutral party.