12au7 tube?

"For $180 you can get a NOS matched pair of Mullards” or pretending to be, more likely..

You speak as if these tubes are easy to counterfeit. Just look to construction and the acid etched codes. RCA black plates are fairly common. Mullards are among my least favorite 12AU7s as are the RCA clear tops.

They may not be actually counterfeit but also probably not NOS by any stretch of the imagination.  I have quite a few in my collection and used to own a well calibrated Hickok Military Cardmatic tester that could actually stress the tubes slightly to look for possible longevity.  So many tested high initially but showed they would only be in service for a much shorter time than one wants to believe.  

Well these are called life tests and should be done on all tubes sold. Most likely they are not by many sellers, especially on ebay. Having said this, a very well respected tube seller advertises "new old stock in white boxes", which translated means white boxed tubes testing as typical new old stock. Not the same thing. The same seller claims that Sylvania Bad Boy 6SN7GT varied in construction and included 2 and 3 hole plates as just on example. 

Best way to tell if a tube is NOS is by a close inspection of the pins. Deep grooves or burn marks are signs of use as is baked on lettering which cant be removed easily with a thumbnail or a wipe. Original boxes arent a definitive sign of NOS condition but they are a good start. Some tubes, like JAN tubes, were bulk packed without original boxes, but this is fairly uncommon in my experience. I have had used tubes which tested higher than actual NOS. Not unusual for true NOS test levels on the same tube type, from the same manufacturer from the same production run to vary up to 20%. So typical NOS levels listed on some testers are averages which arent particularly precise.

These were prices from audiotubes.com, a very reliable source of tubes. In fact, RCAs are $100 for a matched pair.