Just as a precaution, when you reset your device, do it from within your settings menu (not through the bootloader). Apparently, if you have device protection set on your phone, resetting from your bootloader wouldn't thoroughly erase your account information from the phone, and it will require your password in order to boot up the device. Some people are suggesting this may cause problems with the trade-in process. Resetting from the OS settings menu will remove device protection.
I reset my phone through the settings menu as instructed by Google, didn't have any issues with my trade-in.