In the EE community, it's generally understood that if you use ebay or amazon, you're probably going to get counterfeit electronics components. Mouser and Digikey are largely considered safe places to order components from, and presumably they have incentive to maintain their supply chain as free of counterfeits as possible.

For physical goods, I'm more inclined to go to local retailers, since I can inspect them. Case in point, rat traps, I couldn't find a place on line where I could convince myself they weren't selling cheap knockoffs, so I drove to home depot and bought them there. I can't guarantee I didn't buy counterfeit traps, but at least they were high quality.