Hi Joe,
If you are referring to BPO's on short sale investing (buy and resell immediately or buy and hold) as opposed to making offers on short sales in your local MLS, then here is what you do:
Make sure you are the only person that the bank has for a contact for the BPO. I buy my properties in an LLC (for many reasons and I assume you do to), so if I get a call for a BPO, they are not aware they are talking to the actual buyer.
I do not list my properties for a flip until after the BPO is done and currently in my market, not until I am close to bank approval. This prevents the BPO agent form contacting the listing agent instead of me. I also do not put a lockbox on until after BPO as well and let my seller know that if they happen to get a call from anyone that wants to see the house, have them call me.
When you schedule the BPO, always show up, make sure homeowner will be gone, play the roll of property manager, give them realistic but lower end comps, the hardship letter, a list of known repairs needed, and a copy of the offer page of the purchase contract. This is called ethically influencing the BPO. Do not try to push this information on them, but strike up casual conversation and tell them you were asked to give this to them. Some will take it, others will hardly talk to you. If they won't take anything, at least point out the known repair issues.
Also, they want to be in and out and get on with the day so do not get in their way or talk TOO much. I always prefer phone conversation as so much can get lost in translation in email or posting. PM if you would like to speak directly on the phone and I will be glad to share more tips with you.