Your question can refer to a lot of things.
Advice on how to do one? The best way to learn is attend a class on how to prepare a BPO
Advice on whehter or not to do them? Why not? It's extra income.
Advice on whether to accept the order? It depends. I totally dislike it when a BPO is done by an agent who has no clue about the local market. His estimate is what guides the banks on what the market value is, and it can be totally out of whack. I've had requests for BPOS that I turned down because I didn't think I was qualified enough to comment on the area. Sometimes, one street can separate the "good" side from the "bad".
I have a short sale listing wherein they hired a BPO agent from another county. He was too lazy to come, so he asked me for help with interior and exterior photos. I went several steps further and gave him history of the area, market conditions, recent comps, and rationale why some comps will work and others won't. He came back with BPO showing the property value as higher than what the market dictates!
Advice on how much to charge? Some BPO companies charge by the number of comps, the number of photos,. And of course, ther'es a big difference between an exterior BPO and one with interior. I'd say $75 for an exterior BPO with 3 comps is a good average.
Advice on where and how to get on a list? Geez...where do we start?