This is an issue I have run into time and time again. If you bought it on eBay and it was not wiped by the seller, chances are there is still a user account in it and Filevault is turned on. Typically I don't have great luck getting it to display out in these cases without logging into the account.
The touchbar may be blank because that's normal when the device is turned on, but Filevault is enabled and the disk is still locked (encrypted).
Putting it in "clamshell mode" is a good start, but I have even had issues with Macs doing that unless you do a specific dance and say a prayer to the Apple deities. And hope real hard.
You should be able to power it off by pressing and holding the touch ID/power button for about 15 seconds. See what happens if you power off that way and then try to put it in recovery mode (press and hold cmd and R right after you press the power button). If it will go into recovery mode, the external monitor may light up grey and the touchbar should have an ESC button on it. At that point try closing the lid and use external mouse and keyboard.