I was not talking about the returns.
Long time ago, I bought a Tamron 70-300 VC for Canon from a vendor who had good reviews. The box looked like it was opened more than once but the lens appeared brand new. The lens was randomly just switching off if I held the camera in portrait orientation. Working fine in landscape or when the camera was held in portrait "upside down" (grip vertical shutter button on the bottom). I really liked the rendering of that lens so I called the shop to exchange it. They told me they would not send me another lens & I could only process a return. When I returned that lens to them they emailed me asking to call them before they process the return. During my call the owner claimed they put it on three different bodies and it wasn't malfunctioning, and just stopped short of calling me a liar. I later bought the same model lens used here on POTN and had no problems with it.
A hard lesson I learned is that a returned lens that doesn't show visible signs of use would often be repackaged and resold as new.
When I bought a lens on Amazon that appeared decentered (right side softer than left) I didn't even have to explain what my problem was. They just replaced it, no questions asked. It was sold by Amazon, not 3rd party.
With B&H and Adorama, if I have a genuine issue, I know I can get someone knowledgeable enough and willing to help - like Helen or Henry here. I assume it would be a tad harder than Amazon to get a replacement, but perfectly doable. With an unknown vendor, not so much. And the chance of vendor selling me someone else's reject through a discount intermediary is higher.
This still makes it worth the risk if the savings are good. I can deal with potential return if I am saving $ 70. Especially if I am saving a couple hundred. But for $30, they can have it. This is just my approach, it's neither right or wrong.