A BPO stands for "broker price opinion," and it involves using a process very similar to an appraisal.
Companies hire a real estate broker to prepare an opinion of value. The representative of the broker, generally a real estate agent, compares three similar properties that have recently sold to the subject property and adjusts up or down for differences. The final result in an opinion of market value.
Broker price opinions are sometimes controversial, especially if the agent preparing the BPO has little experience or knowledge about the neighborhood. But BPOs typically cost less than a full-blown appraisal.