My PBP starts up like a 1977 Chevy Nova

[TRS-80]

Incidentally -- and I ask this purely out of curiosity with no judgment about pine64 or the pbp -- why do you guys have such faith in the hardware? I mean, I know lots of SD cards and power supplies go bad, and lots of people mistake those for bigger problems. But this pbp _came_ with a bad keyboard that had to be replaced.

Speaking only for myself, it's not that I have faith but rather that you want to make sure to eliminate all common problems first in your troubleshooting process.  Even the most experienced of us have been bitten by this.  It is not by accident that the page I linked is referenced so frequently (at least in Armbian forums anyway) and they gave it such a prominent place in the documentation and troubleshooting sections.

Quite the contrary, you can find a number of threads around these (PINE64) forums about faulty hardware, from (often seemingly) knowledgeable people who are not simply griping.  Therefore, in fact, I am not sure how much faith I actually have in Pine64 hardware, after all... 

Given PINE64's parsimonious return policies, I think is all the more reason to make absolutely sure it is hardware issue before pursuing that (difficult?) route.  Unless you want to just say "to hell with it" and purchase another one...

Also, generally it just hasn't been my experience that the quality control on electronics is very good. I used to order computers and IT gear for Harvard, and my rule of thumb was that 1 in every 10 things we bought was shipped to us broken. Didn't matter if it was a $20,000 Sun server or a dumb little vga dongle. I've been out of that game for a long time, but it doesn't seem like it has improved much. For the last nonprofit I worked for, I ordered 10 mac minis, and one was shipped to us broken. 

My pinephone and my raspberry pi work great. I feel like I was kinda due for a lemon.

I think this point of view is very valid.  Personally I still want to make sure it's none of the basic things, which it sounds like you certainly have, by now.