I don't know if this one could be fix and maybe they should allow there user to set their own preffered fee so that the user can set according to what they like.
Most gambling sites don't have that feature. And it might become a problem if users can freely set their preferred fees then in the end it will get stuck.
Betnomi does not charge the user any fees for withdrawals as per their FAQ.
To save fees, only choose coins with less transaction fees. Betnomi has a great number of supported coins with less transaction fees.