littledog said:
You probably wouldn't buy a used car without a test drive and a thorough evaluation - especially an expensive vintage one. Sure, you probably COULD turn around and just sell it to someone else if it is a lemon, but most of us would feel some ethical qualms about scamming someone. And if you make full disclosure, you probably won't get back what you paid, if you were assuming it was a working piece of gear in good condition when you bought it.
That's why you check the feedback ratings and contact the seller in advance. If the seller has more than, say, 50 transactions without a single negative or even neutral feedback ... then it's a good start. If he/she returns all of your email questions promptly, and even provides a phone number and speaks perfect English over the phone

... is very upfront and knowlegable about the condition of the mic, etc. Then your chances of a bad experience are pretty miniscule.
But ebay is only one option. There's also Craig's list, or even the local entertainment paper (assuming your city has one). If you get lucky, you might find someone locally who will let you stop by and test it out in person, same way you might do with a used car.
This is just one way of doing things, and not everyone is going to be comfortable with it, nor is it going to fit in to their personality style or "psyche" or whatever.

Some people's brains just aren't programmed to be comfortable with such a concept, and that's totally okay.
If you happen to be one of those people who has to have the reassurance of a warranty, and having something in new condition ... then retail is really your only viable option. And for that person, you just have to be smart and creative in how you go about your purchasing decision. I, personally, just don't feel in the least bit comfortable buying something very expensive, strictly on the advice of another person. Knowing full well that if I wind up not liking it over time, that I will only be able to recover a fraction of what I initially paid for it, due to the fact that it's value depreciated significantly the second I took it out of the box (or "drove it out of the lot").
.