The soldering quality is decent. After checking all the VIN traces, the only thing I can identify is the relay’s upper-middle pin (close to the top edge of the PCB), there seems to be a solder ball that touches the nearby trace. Normally this isn’t a problem, since the traces are all covered by solder mask, however, sometimes the very edge of the trace may have copper exposed, so if you have a solder ball touching it, this may lead to shorting. I suggest using your soldering iron to reflow the relay solder joints, and re-check the VIN-GND resistance. If you still can’t figure out, send an email to [email protected] and we can see what we can do to help.