Personally, I would still value this cat rather high! People who want a black mink for the mink look may not want it, but people interested in breeding point gene cats would still find them very valuable. Especially someone looking to breed high white point cats, who might breed this kitty with a mid-range left/right cat for the cute face patterns!
Well, I am technically in the market for cats like this, so definitely try to get a second opinion, but when I got a G1 LH no white black mink I traded for
roughly 30k in value (with offers that were technically higher but less desirable to me than the eyepatch kitty I traded for) so G1 no-white SH would be 20-25k based on that, but in actuality could go higher.
I like cats with fun hidden patterns, and I know others enjoy having cats that hide point as well because failed beans may still have point gene to lift their value. Since your kitty carries non-white and longhair, it can feasibly make no white mink beans which would sell for a fair amount. I believe G2 SH black minks go for 12-18k depending on if they're trade wind or not? And since eyepatch cats have a happy niche market, that can attract some users also.
Also your kitty is BBFD4, or doesn't carry orange, which is extra valuable to people who only want to breed black or grey-range cats. So even taking into account the fact you can't see the cute mink face on this kitty, don't sell yourself short! There's still a lot of breeding potential that would be perfect for many users who have more intricate breeding goals! If I were you, I wouldn't drop the price because despite the hidden face the genes are still really
really good. Aim for higher range offers and see what you get!