I use 6189W tubes in amps and they sound great. It is a NOS long life military version of the 12AU7. These tubes are put through more stringent quality control test than regular tubes.
When you buy a tube from a tube seller, you get a warranty. The estate sale people are not offering anything so their asking price is high. It is a gamble on your part but since it is only one tube, you aren't risking that much.
The problem with an untested tube is you don't know what you are getting. Is it unused or has it been in service. If they can assure you that it is unused and that it works, I say go for it.
Here is what the tube sells for in the US: http://www.tubesandmore.com/search/node/6189W