There are some general guidelines here https://guides.brit.co/guides/spot-fake-dr-martens-boots/particle-9, but in order to get a refund (in case they are really fake) you will need to have the shoes certified by an authorized person, as others have said. Personally I have no idea as I have never owned a pair of these boots.

PS: They seem to be a reputable seller. I am sure that if you have concerns you can talk to them directly.