I just accepted a quote from PowerOn.
It was quote number 96880. It was for a Mac Pro 1,1 vintage 2006. It was model MA356LL/A, which is a quad-core dual 5100-series ("Woodcrest") Xeon 3.0GHz, about 4 1/2 years old. It had 16GB of DRAM, the most that particular model could take.
I used it constatnly with few problems the entire time I owned it. I had (2 years ago) upgraded the video card from the original ATI very hot card to an NVIDIA 8800 model Apple was selling especially for the Mac Pro 1,1. Apple's original 500GB hard drive failed last year, and I had replaced it with a Seagate 1TB drive that as of two weeks ago reported no errors or problems and no replaced sectors or pending bad sectors in the SMART utility. This 1TB drive was in the machine when I sent it to PowerON, the original bad drive had long since been recycled.
I upgraded both original Apple "superdrives" with (now discontinued) Pioneer 117D's, which were essentially in brand-new condition.
This computer was far from new, but it was still serviceable and was working just fine when I secure-erased the disk and re-installed Snow Leopard before shipping it to PowerOn on the 9th or 10th of September (i.e. less than two weeks ago).
Power-on's original quote based on my description of the machine as "good" was $740.54.
Power-on's "audit" determined that the condition of the machine was "poor" due to what they described only as a "defective system board". Exactly what the defect or problem was, was not specified. No further details were given. I have no idea what problem they discovered. I know the machine was running when I sent it to them. It's entirely possible that an exhaustive hardware probe turned up a problem of which I was unaware...but it would certainly have been nice if they had bothered to tell me what it was. It was a running computer with a lot of memory.
After the "audit", Power-On revised their quote down from $740.54 to $215.88.
I accepted it mostly because I just don't want to mess with it any more. I have my new Westmere 6-core mac pro installed (and I love it, by the way), and don't feel like wrestling with any more 60-lb boxes. If I had them ship the old computer back, I would just have driven it to my local recycling center. I don't like ebay, especially with used computers. I think that this attitude is common, and that PowerOn and similar enterprises rely on it.
I make no judgment or generalization about PowerOn. I am simply providing all the information I have concerning my own single recent transaction.
I personally would not use PowerON's service again, but this is just one person's experience.