Broker Price Opinion (BPO)
A broker price opinion is an estimate of a property's likely sale price prepared by a real estate broker or agent rather than a licensed appraiser. Lenders and servicers order them for defaulted loans, portfolio reviews and some refinances. Investors often get an informal version from their agent when screening rentals by gross rent multiplier.
A BPO leans heavily on comparable sales, the same raw material a GRM uses. Some BPO forms also ask for a market rent estimate on rental properties. When they do, the broker's price divided by the broker's annual rent gives an implied GRM you can check against the market range.
A BPO is cheaper and faster than an appraisal and follows fewer rules, so quality varies with the agent. If a BPO and your own GRM work point to very different values, compare the comps each used. The disagreement usually comes from one side picking sales or rents the other would not accept.
Further reading: Broker Price Opinion (BPO) on Wikipedia.