The higher the asking price the higher the need for a professional certification. " money back guarantee if it does not pass a certification " is not a valid proof of authenticity.
As to the type, it's a beauty!
My non professional guestimate is an Ensor OR Fairland. You can select your own preference based on a couple of real examples.
For Ensor example, see page 2 of this message bd......under heading of " BIG FLINT FROM C3 ". Thats been COA'd by D.R. as being ENSOR
FAIRLAND......frt pg, top R.....open " weekly archives "....about 10% down on the L,,,,a very big specimen.
Notice how the sides bulge out slightly toward the distal end. That is not characteristic of either Ensor or Fairland but is usually evidence of artistic license taken by the knapper who made it. It is nicely made and I would value it at $10 an inch.