Why Purchase used tubes?

If you are certain what particular tube(s) you favor in a given application, and you wish to eliminate as much uncertainty as possible, by all means buy NOS. But those sellers you can trust to offer genuine NOS are not cheap by any means. I've gambled on many, many tubes on Ebay and seldom been burned, most are suitable for my preamp's line stage duty. I've been able to sample a dozen 6dj8/6922 flavors via Ebay for what one or two NOS tubes from a primo seller would cost. Phono application, a different story. There, it's cheaper long term to just pay a reliable seller for tested NOS I think. Which brings up the factor of how hard a given bit of kit burns through tubes. A lightly stressed application can be considered differently than a highly stressed one.

Warrenh, looks like you've been spending time reading Joes Tube Lore. If so, remember that his picks are based on HIS equipment. His greatest enthusiasm is reserved for Amperex offerings. In my system, I find that some of Joe's favorite Amperexes appeal to me less than Siemens 6dj8's from the 60's. Before I'd ever blow $560 on a pair of tubes, I'd be sure I liked the "house" sound. You can pick up Orange Globe Amperex 6DJ8's (assuming you can use 6dj8's) for a song compared to the most coveted Amperexes. I agree with Joe on those tubes, I think they're great. As to the price of pinchwaist d-getters, "fair" doesn't mean anything, we live in a free market economy. There's a very finite quantity of a highly coveted commodity and if people will pay the asking price, it's unrealistic to expect altruistic pricing. It's all a matter of perspective on the worth I suppose. To me, I don't think the difference between the "best" tube and close contenders is worth hundreds of dollars per tube. Others obviously feel differently.