You got burned BIG TIME.
Read this link about buying used devices --> The All Too Common SAD Reality of Buying … - Apple Community
The bottom line is the device is 100% useless without the Apple Credentials used to set up the iPad. Since you can't reach the jerk who ripped you off and you do not possess the original purchase receipt with the iPad serial number on it, there is NO way to bypass activation lock. Apple will NOT help you. We cannot help you.
If you can't get your money back, which you most assuredly cannot, the device is ready for the recycle bin.
I hope this wasn't an expensive lesson. Next time NEVER purchase an iPhone or iPad you haven't validated is completely ready for a new user.