One thing to be aware of when buying one used that I just had to go through is that you can't really get them serviced if anything breaks. Herman Miller gives

One thing to be aware of when buying one used that I just had to go through is that you can't really get them serviced if anything breaks. Herman Miller gives a 10 year warranty that they'll fix the chair if something happens to it. I bought mine about 8 years ago from a co-worker who acquired twenty of them in a dot-bomb auction. It's been awesome, but a few days ago the piece holding the armrest to the back broke, so now I only have one arm-rest. If I had bought it from a retailer, HM will fix it for free. Even so, 8 years of having it prop me up and this is the first issue I've ever had with it, so I still recommend it.