Retail refurbished = Ok.
Online refurbished = Not Ok.
This is from my experiences in the past with refurbished machines. Retail operators run more of a risk dealing with unhappy or aggrivated customers if the machines break down. Even if there's a disclaimer saying that "Machines are only guranteed for 30 days", retail refurbished machines always usually have the "least" amount of defects. Most of the time, it's a bad component that they simply swapped out of a perfectly otherwise working machine. Also, cosmetically, retail refurbished is usually quite clean.
As for online refurbished... I've had horror stories I rather not say.
EDIT:
I also forgot to mention. Manufacturer refurbished equipment is the best you can possibly buy when it comes to anything. For example: HP refurbished printers are as good as a brand new one. If the machine or part is refurbished by the "store" that is selling it, I would be a bit more cautious.