If you had a dozen pairs of classic vintage ubes in your closet

All the Tubes apart from one,  I have purchased over the past 2 Years have been purchased as NOS Tubes with close to the manufactures measurements being presented by the Vendor.

I have purchased under a agreement they are tested when received at my end, and can be returned if the Tubes do not measure to a acceptable standard on a friends AVO Test Machine.

I have had to return Valves due to low measurements and the offered exchange Valves also showed low measurements.
This was the Vendors proposal as a resolve before a refund was made.
I am fortunate to have used Vendors who are willing to honour such prior made agreements.

This purchase arrangement has been put in place for ECC83, E88CC and 6SN7, with the ECC83 being the Valve that has been the one needing replacements and a refund.
I bought a Early 60's E88CC from Japan (no return) and another from Germany (return arranged) about Six Months Later, at about 40% of the going rate for a matched pair, both measured close to the Manufacturers Guide, so this was a Punt that worked out as the Japan Valve was very cheap and was added to a package that was being produced for export by a Buying Service   

For the Buyer the Market does demand an attitude of Caveat Emptor.  

@lewm.....   you have a point.  My ears have told me when it is time to change for the last three decades.
@pindac     ..  there was a time when NOS meant New Old Stock, not that the tube still reads close to new.  I'm talking perfect old lettering and pins that look like New Old Stock + a tube test.

You will most likely not be able to consistently tell a used tube from new with a simple emissions tube tester. Shorts yes and that is about it. If you buy a tube tester buy a true transconductance tester. Many Dynamic Mutual Conductance testers only test for transconductance on some tubes (B7K 707 for example). 

It is also true that suitcase testers do not test most power tubes are real world levels and as such they do give these tubes a true test. I have found that gm testers like Hickok and Triplett do a fine job on everything but power tubes. 

Most often, these days, the vendor himself did not own the tube from "new", meaning he did not buy it from one of the old time businesses like Radio Shack or Heathkit that once had brick and mortar stores and sold truly new tubes over the counter.   So the seller only knows that the tube looks new and has a proper box to go with it.  That is why I would value sellers that have their own high quality test equipment and are willing to warrant that a tube tests within new specifications.  There are a few out there.  But how did this get into a discussion of fraud in the tube business?  I thought we were talking about the impulse to tube roll.

I have a lot of NOS tubes, in baggies, by type.  I use them as replacement for Gold Lions reissues that fail.  I keep waiting but none of the 12's will fail.  I quit buying NOS Tubes maybe 15 years ago.  Price vs. Performance became an issue as the product became more and more scarce and costly.  Looking back, I was buying NOS tubes to make gear sound better so, I just started buying better gear LOL.