Selvam
"Oh excellent, excellent" Nira Melubb says. "If you wish to convert your coins to jewels I'm well equipped to accommodate most transferrals... for a small fee of course. If you wish simply to store your wealth here I can assist you as well, free of charge, though there is a small fee to be paid for any withdrawls... Guarding people's wealth isn't free after all.
The man proceeds to explain the costs of his services: He will happily exchange coins and metal for other media (including precious stones, charging only 10% of the value exchanged. In other words, if you one were to convert 600gp to stones, he would give you 600gp worth of gemstones and other valuable material, for a fee of 60gp.
If, on the other hand, you wish to simply deposit your gold in a safebox it costs nothing, but when you go to make a withdrawal and retrieve some of your money there will be a fee of 10% of whatever amount of coin you withdrew, which can be paid from the money withdrawn, or paid with money still be kept safely. So if you have 600gp deposited with the moneychanger and you decide to withdraw 100gp, it will cost you 10gp. You can pay this with the money you withdrawn (meaning you give 10gp to Nura and receive 90gp), or you can pay it with the coin he's still keeping safe for you (meaning you'll get 100gp in hand, and have 490gp remaining in the bank after paying you 10gp fee to make a withdrawal).