The first and most elementary that comes to mind is to look at the packaging. It will always be written who the manufacturer is and what name of the drug is. That is, it is clear that the original Viagra is produced by Pfizer, which is why the images with the word Pfizer will be printed everywhere, including a blister with tablets and often even tablets themselves.
2. The site may contain content, the use of which may have potential risks and be harmful.