MBP trackpad not working, but Apple (store) got it to work during reinstallation of macOS MacBook Pro (Retina, 13-inch, Mid 2014, macOS Sierra 10.12.6). 

My built-in trackpad can click (sometimes) but not point, scroll, zoom, or perform gestures, so I have to use a USB Logitech mouse.  

I took it to Apple and after they checked some settings they were not able to get it to work. I decided to have them erase everything and reinstall macOS. During the process of them installing the OS again the Apple guy was able to use my trackpad just fine! I said Oh you fixed it. Then after it was installed it did not work again! So it must not be that it is broken inside. 

I asked him how can that be?? He said when it was working it was because it was being accessed through Apple's side and it must be something in the OS preventing it from working. 

I do not know if reinstalling the OS still keeps disk image checksums, folders or system preferences accessibility settings. 

What settings should I check or what Terminal commands could I use to try and get my trackpad working again?
Reinstalling OS X will keep your previous system preferences set up.

Trackpad could be disabled in the System Preferences Accessibility.
Since in your case you had the Logitech plugged in, the system just did what it was asked and disabled the trackpad.


  USB Receiver: Product ID: 0xc52f Vendor ID: 0x046d (Logitech Inc.)
  Version: 30.00 Speed: Up to 12 Mb/sec Manufacturer: Logitech Location
  ID: 0x14200000 / 14 Current Available (mA): 500 Current Required (mA):
  98 Extra Operating Current (mA): 0




Solution: Disable the check mark in the system preferences Accessibility.