Now that the first "what if" scenario is out of the way, let's consider another one:
If it can not put out its rated power with good voltage regulation, low noise/ripple, and/or is overly loud, or has less than a three-year warranty or the company can't be relied upon to stand by their warranty, I'd pay literally nothing for it. Not even $5 in hopes of reselling it for a profit, because it would be downright immoral to sell a PSU like that. Unfortunately, most no-name PSUs fit this description well.
Moral of the story: you are going to have to test it with a load tester and oscilloscope, or find a person or article where someone else did, and get some more info on the company, product, and warranty to determine what it's worth.
Let's keep in mind you can't go by brand alone. When evaluating the value of a PSU, it must be considered on its own individual merits. I've seen awesome OCZ and terrible OCZ PSUs, for example. Same for Rosewill.