Steam rates are usually around 70-75% when payed with bitcoin.
Kinguin is in the category of G2A (key reseller), so your rate should be lower. I'm only saying should, because there are more discounts on Kinguin then on Steam, but keys might get revoked in my experience.
I think there is kinguin buyer protection that you can avail. But still, I can consider good offers from anyone if you feel the rate is high.