I have used the same place as Winston, above. It is a real, bricks and mortar, drugstore that I have gone to in person as well as ordered on-line.
I didn't check the link on how to assess such places but I did do extensive research several years ago before deciding on Petpharm. In the course of looking I did find a suspicious operation in Winnipeg and alerted the Health of Animals people in Manitoba. The place was claiming an empty, abandoned warehouse as their mailing address and was using someone claiming to be Veterinarian who was not licensed to practice in Manitoba. I never found out if he even was a Vet and I never found out the outcome other than that place no longer pops up on internet searches. Not in that guise anyway.
Many big pharma have sections on their websites that show you how to look out for counterfeit or stale dated product. Be careful, do your research.