Get SD cards from B&H or Adorama. They serve the pro photographer community, who are ferocious about storage quality largely thanks to war stories from 20 years ago when flash memory really was a crapshoot - also why any new camera body released with only one card slot provokes a million old dudes to fuss about that one wedding shoot they lost in 2003 or whatever. But in this case it's to your benefit, since the media you get from those sellers will be what they say it is.

(I get mine from Micro Center. Kinda feel bad about not going to my local camera store, but the guy who owns the place doesn't really seem at home with technology. I don't even know if they carry UHS-II cards, but I get all my used gear there, and with the margin on that stuff it's not like I'm hurting them by getting a $80 SD card elsewhere...)