First, I have no clue! Secondly, and the reason I'm posting is, a national BPO company will likely cost more in the long run and you'll acutually end up having many of the same local providers doing the work. This has to be the same as Lenders Services Appraisals or any other appraisal company. They simply contract with apprasiers for a lower price, get a job and sub it back to the guy you could have done it in the first place....all you need to do is negotiate the price! In my business, I had a short list of appraisers, 5 and three I kept busy, for that they cut the price and tried a little harder I know. I suggest you keep it local if you can.
If you are one who buys or does business all over the country, surely you have areas of your operations. I would then suggest you do the leg work to get locals to do the work.
What I found with the national companies was that they were more expensive, took much longer, did not have a sence of providing individual service, were not as receptive to second opinions or making adjustments and had billing departments that didn't know what the right hand had done.
The time you spend in putting a relationship together in local areas will save your time and money.
Then, if a deal pops up where you don't have that covered, farm it out. IMO, you could use a dart board to make the decission and try them out. While you will probably pay more and take more time, chances are there won't be alot of risk in them not getting it done, but how well it's done might be an issue, each would be different in different areas, just depends on the luck of the draw, IMO. Good luck!