I think is fair to charge for the review, after all you are spending resources reviewing the site.
What I don’t find fair is that review fee is the same value as the submission value.

I think that 30%-50% of the submission value could be a more fair value, but also depends on the total value.

Normally less established directories don’t implement a review fee, because they are afraid to lose submissions, the bad thing you get bombarded with MFA and other low quality sites.

If the cost is a few $ then fine. But when they are asking you for £300 it is a little rich IMO.

I think I agree with both the above arguments, but review is a very subjective thing that is why I am not sure about non refund ability. A site you may find fascinating may not be considered in the same light by another editor.