Tube experts ---Chime In Do BK testers Lie?

Recently I ordered 50 Sovtek 6550 tubes from a seller on ebay. I later found out the seller was a former employee of Audio Research who bought their stock of 6550s which were overstock from the 90s and never used.

I received the first box of 25 tubes and using my tube tester, a BK DynaJet, about 18 of 25 of the tubes tested in the questionable range. I emailed the seller and he said, the tubes were good, he has sold thousands to others who have re-sold them, and I was the only person who complained.

I was waiting for my 2nd box of 25, and he suggested I use another tube tester since mine may be wrong and is not very good. I recd the 2nd box of 25 and took now 50 tubes to a local electronics store and used their BK DynaJet 707, which is a machine they test all their tubes on....

Box 1---on their tester, now 20 of 25 tested "questionable"
Box 2-19 of 25 tested "questionable" on their tester.

I email the seller who now sort of alleges that even though I claim I have 20 years of tube experience, I don't sound like it. He offered a refund, less my shipping costs to and from, less my PayPal fees. I lost about $80 on the deal.

I get my refund today and read his PayPal remarks, and in bold, he claims all the tubes I sent him test NEW on his Hickok tester. for a fact, there were at least 3 which were plain DEAD on both my testers...

My question, do you think BK testers can test a tube to be bad, when in fact they are not? Does BK tube testers have issues with testing 6550s?,

I am glad to get past this situation, but really am a bit peeved at this seller, I was only telling it like it is for my perspective and 2 tube testers results.