A deposit fee would be needed absolutely, but if we're going to get into variable deposits I'd suggest instead of charisma make it appraise. Tellers have their rules still and can't just say "Oh you're pretty" or "Oh you have a strong personality" and just skip out on the fee. How will they explain to their boss why the vault has X amount of gold but only Y amount of commission was taken? Appraise is the 'trading' skill though, so if this deposit fee was to be impacted by anything I think set values of appraise should be it, as recognition for local merchants holding some kind of business accounts. People with high trade skill would be doing higher volume deposits and they'd be making their money by that volume rather than rate, with the lower rate as incentive to use them instead of other means.
That's just my opinion if variable deposit fee is used at all. Easier to just say 5% or 10% for everyone across the board. Also deposits at set intervals. 5k, 10k, and 15k deposits. Maybe higher rate for smaller deposits and lower rate for big drops. This ensures that players always have SOMETHING on them and don't just use the bank as a second inventory, and that there is both reward and risk involved in saving up higher ammounts of gold to deposit in bulk transactions. Withdrawal can be any spoken value though.