How to Spot Fake Supplements and Protein Powders Online

I just bought a tub of protein from a third party seller on Amazon and the seal looked a bit dodgy. The powder also has a different texture than what I am used to. I am worried that I might have bought a counterfeit product. It is so hard to tell these days with how good the packaging looks.

What are the red flags I should be looking for when buying supplements online? I am in the UK and I usually try to buy directly from the manufacturer but sometimes the deals on other sites are too good to pass up. I have heard that some people find literal flour or sugar in fake tubs.

Do you have any tips for verifying the authenticity of a product? I am thinking about reaching out to the brand with the batch number. I would love to hear if anyone else has been burned by a fake supplement and how you handled it.