I recently Prime-purchased some combo shifters that looked like Shimano, but were no-name on the description or pictures. What I got in the mail was counterfeit Shimano labeled shifters of really bad quality....brake levers wobbly, barrel adjusters wonky, etc. I sent them back. Easy lesson learned without the cost of owning them.
I have made a lot of purchases on Amazon, and I usually have no regrets. When you need to sell a bike, Saddles and grips are very cheap and of decent quality (but not so comfortable) I found decent brake pads too that seem to hold up just fine.
On the other hand, pre-pandemic, I would almost always find what I was looking for in the cheap at my LBS that sells UltraCycle parts. No frills, cheap, and decent...not pro stuff, but you get the drift.