A BPO is the opinion of property value given by real estate agent or broker.  The BPO is an estimate of several variables including the selling price of property based on condition of the subject house, selling prices of comparable homes in the area, neighborhood condition, overall market condition, etc.  These values can vary and that is why it is critical to know how to influence the BPO.  This process is often used in the place of a full appraisal when a property goes into default and considered for loss mitigation.  As an investor you want the BPO to be reported to the servicer as low as possible.

The BPO is the single most influential variable that the lender considers when  deciding how much they are willing to accept as a reasonable short sale offer. If your offer is not in the ballpark of the BPO, it will most likely be rejected.  It's not that the lender is not willing to accept a short sale; it's that the short sale offer does not come close to the amount of the BPO.  So don't give up and continue to negotiate with the BPO to come to a reconciliation of a reasonable price offer.  

If you can work with a full BPO, the better your chance of having one on one and direct communication with him.  He will do a full inspection, thorough assessment of the house, sometimes, the lender could even send an appraiser as opposed to an BPO. 

Compile comps, estimated costs of repair, and any other relevant information that will justify a discount. Identify cosmetic repairs such as wall damage, carpet, paint, etc.  Then identify potential repairs (may not be readily seen with their naked eye) as in roof and water damage, faulty plumbing or electrical fixtures, pests, mold, etc.  Have a breakdown of your repairs, associated cost, and be able to explain how you derive to your estimates.  You should do all your homework prior to the appointment with the BPO.  However, during the appointment, be open to his/her comments.

You and BPO are the only two should be having conversation about the property.  Leave out any opinion of the homeowner .. It just adds lots noise.  Unsolicited comments could only create more complexities and slow down your time with the BPO.

Take pictures of every room in the house and remember to be more thorough then the BPO.  Point out the most important repairs only (likely to be most costly) and make him aware of other homes in the area that are comparable to your offer. By doing your homework and come prepared, you will build a rapport with the BPO and will earn respect with the BPO.

Before the BPO leaves, ask him to give you an indication of the ball park estimate they may already have in their head.  They may or may not give to you right away because they have to tabulate all the numbers and complete their report.  (It doesn't hurt to ask)   Ask for a follow up .. The BPO may not agree telling you their report is proprietary to the lender.

Give the BPO your opinion.  You will be surprised as to how much your opinion matters!!  You are likely to know the neighborhood, school, crime rate, employment, etc, more than they do.  Let them know what you think the property is worth.  If the BPO sees you as someone who is knowledgeable about the property and the activity in the neighborhood, your opinion will be valued and taken into consideration when they make their report to the lender.