Followup: I spent a bit of time looking for reviews of OTHER gas pool heaters on Amazon:

StaRite Max-E-Therm 400
Sta-Rite Max-E-Therm Black 400
Pentair Minimax 100
Pentair Minimax 100 Millivolt
Pentair MasterTemp 250
Zodiac Legacy 399

Most others hadn't been reviewed. I didn't read most of these reviews, but I still saw several where it was obvious to me that the purchaser made the error.