Seeker,
I buy most tubes from ebay and can't recall a bad tube experience I could not resolve.
Here is the way I understand it.
It is set up so that user satisfaction matters, and seller ratings are clearly stated. This in turn effects their future at ebay, bad and good impressions from buyers being clearly shown, and selectable to read. Associated, it seems that if buyers are not happy, it costs sellers more, in part because disputes cost ebay, and in part because ebay wants to "encourage" good sellers, and discourage bad ones.
Even with careful buying, with old tubes, now and then some will have problems. They can make it through a test fine, and still show problems, even failing after some use. But most I have gotten have been great. I have had
new tubes fail early too.
And when things are not right, a noisy tube, loose base, or one that goes bad, sellers I have bought from have been concerned with setting things right. With clear explanations of the problem, verifying by changing channels on the amp, etc, I have had good luck resolving occasional issues, getting matching replacement tubes, or a refund.
One time of many tube purchases, the seller knew a lot, but was slack in selection. I was just getting into 807s and seeing a matched pair I liked the look and price of, I contacted the seller and asked if he could make up a quad with matching construction and scores. We set it up, and the tubes sent did not match in construction, one not even working right. When trying to sort it out, the seller dropped the ball, and ebay picked it up. I got a quick refund and a mailing label to return the tubes if I recall correctly. That was a pain, but resolved, and a 1st and last for me where the seller did not work it out fairly on their own.
I have bought from the seller you mention a few times with no problems. But this reminds me...looking carefully at what I buy helps assure contentment! This seller seems to be pretty accurate in matching construction, scores, and often the same or similar date codes, but the labels may or may not match. For example
http://www.ebay.com/itm/2-matched-1964-66-Mullard-RCA-ECC189-6ES8-tubes-New-Old-...or:
http://www.ebay.com/itm/2-matched-RCA-Tung-Sol-5V4G-rectifier-tubes-Black-Plates...This is a case where the seller seems to know what they are doing, apparently focussed on function and sound more than matching labelling. If labels matter too, this is just a good pointer to look carefully at what is being sold. I also really look in detail at construction...for example, on a rectifier say, sometimes the internals may be just alike, but the bottle a little different....the top mica on one being notably closer to the bottle top upon closer inspection. May not have much effect, but it might, being different productions.
This points to a safeguard on ebay. If a buyer feels something is not as described, both ebay and the seller loose too. So like this seller, many have good explanations and pictures. But sometimes less pro sellers have nice tubes at nice prices, and not necessarily good pictures or all the information. That is when I ask questions.
Some sellers will have matching scores, and labels close or matching, and not quite matching construction. This is usually a bigger deal to me, sound being primary, and matching construction, scores and dates help ensure matching sound.
But then, some years ago I got one pair of Mullard E88CCs (on sale from partsconnexion) where the construction was a little different, but close, the getter riser on the parasol getter long on one and short on the other. This made the silver getter flash go lower on one than the other making it obvious. Otherwise, the construction looks identical. Also the date codes looked like the same factory, but different dates, best I can tell, 63 and 69. Finally, the test scores were very close, apparently a priority of the seller, long time tube users themselves. I have been using this pair in my CSP3 for a long time with many others to choose from, so I obviously like them. But even so, this taught me that I prefer the assurance of relatively close matching scores, construction and dates for a true match.
Some sellers don't have testers, but the tubes could be NOS, matching, and really good..... I have bought some real deals of 5 packs of inputs like this, and maybe lucky, but testing them at home, they have been good matches, literally the same production right off the line and into the box sets.
Some good sellers are audio heads selling off part of their collections, and know the tubes, bought carefully. They may have the original test scores and not current ones, but know how little they used them, and decent prices.
Many sellers are quite professional, matching test scores, construction, labels and dates pretty consistently. I find this especially with some European sellers.
The cool thing though for us, with sellers variability, price is extremely variable also, and price is usually relative based on scenarios like I have mentioned. But then you find sellers who have great stuff, careful matching, and sell high, and some who sell the same basic quality low.
In general, I look carefully at the seller ratings.
Also, I look carefully at the construction and appearance of "matched" "NOS" pairs, and test scores.
And if I have a question, I write and ask. Sometimes a seller will say, test great," "matched" and/or NOS, with no scores, and when asked can provide them.
The bottom line for me. I search a certain tube type every so often on ebay and compare availability and prices at the time, looking at all these things. I always wait for good pricing on a tube I want, so check in regularly.
Often off-label tubes can be a good buy, like GE labelled Mullards, or CBS labelled Siemens. For example, I have a few pair of really good input tubes, early 60s Siemens ECC88s that were $40-60. If Siemens labelled, the same dates, scores, and construction, they might be two or three times that.
I like ebay for tubes. With care and attention, get nice tubes inexpensively there.