I ordered a BM235 off of Amazon back in September. After it arrived, I noticed it was reading low on the AC and DC voltage ranges compared to other meters. At the time, I didn't have much spare time to investigate, so I set it aside. I finally got back to it this weekend and took a closer look at what was going on. I'd often get zero readings at low voltages (i.e. below about 10 volts), and then for higher voltages, it would read low (e.g. 40V for a 240V source). I also discovered that touching the buttons (not pressing them, just touching them) was often enough to change readings, sometimes resetting readings to zero and sometimes making them accurate.
I took apart the meter and discovered that R12 (edit: I initially said R18, which was incorrect) was loose. It's a large, through-hole resistor, and jiggling it a little, it came completely out of the via. It looks like there was no solder on that leg of the resistor at all. The attached images show how clean these are (the via above the SW5 lettering is where the leg should be).
I soldered the resistor into place and that seemed to fix the problem. I had to recalibrate the temperature range, but otherwise the meter seems fully functional after the repair.
Anyway, I just thought that was interesting and maybe this would be useful if anyone else is running into a similar problem.