For Merchant Fees that we pay when clients pay by credit card, would I be correct to assume that those get grouped under banking fees?

Yes, merchant fees would be grouped under banking fees. 

Yes, merchant fees for credit card payments can be grouped under "banking fees" if that's your existing category for bank-related costs. However, for clearer bookkeeping, consider creating a separate line item like "payment processing fees" to track these expenses specifically—it’ll help you analyze the true cost of accepting cards. If you’re using accounting software, check its default categories (they often have a dedicated spot for this). Always double-check with your accountant if tax treatment is a concern!