The initial message was a fellow was saying that speed tests were showing bufferbloat, but his ISP said all was good. There were multiple interchanges - here's a summary:
I started to say, "Maybe things are OK then..." and he said, "Well, I'm a gamer, and bullet registration is off..."
So I asked for a Waveform test. In true non-believer fashion, he asked, "Is it possible to have bufferbloat on X equipment?" I said I don't know - run the test.
He did, and he did (have bufferbloat - a bit). I explained how a bunch of 60-110msec samples might be enough to cause his hits to go awry.
We were about to get to the question I dread: "How can I fix this?" This is the leap-of-faith moment, where we end up saying in essence:
Your vendor(s) lied to you. You can fix this yourself. Just buy a spare router and install some Open Source software...
I always fear this moment because there's such a high likelihood of getting egg on the face from one or many of the reasons listed in the original post. If they happen, I usually slink away, and say to check the "What Can I Do About Bufferbloat" page.
Fortunately, he had a Ubiquiti UDM Pro, so he said, "Hey, I turned on smart queues and it looks way better." With that sticky point out of the way, there were several more interchanges where I got to say that both the router and the Wi-Fi can create bufferbloat and that these bufferbloat measurement tools are only broad indicators of "network goodness".
So this is one circumstance where it worked out. But I ache to have some advice to address the dread-causing question. Any thoughts? Thanks.