Just stay away from those "hustlers" that will tell you that Japanese tubes are better than Telefunken or Amperex!
I also had the experience of buying 12au7 tubes from a local seller that went bust after 3 months, and I bought it from a reputedly "honest" seller from another local forum!
Not only 12au7 tubes, I got some 6x5 tubes from a local seller that gave my preamp oscillations which took me a couple of months to isolate.
He also sold me some Siemens caps that leaks oil, upon checking, those old Siemens have PCB in them.
Latak na yata ang binebenta nito.
The best insurance is to have the tubes tested before handing over your hard earned cash. In fairness, there are a lot of honest sellers. Get from those who are willing to give you warranty.