If I were buying used tubes I would ask the seller if he has tested them and what tester he uses. Some people that sell tubes are liquidating their stock because they changed gear. With the exorbitant prices of tubes I would be more inclined to buy used if the seller answered all my questions to my satisfaction. Some sellers that espouse to be "tube gurus" have sold tubes that are faulty and the sales pitch is over the top. Bottom line is, will the seller stand behind the product. With the decreasing avaliabilty of NOS tubes "used" will play a more important role.
