ACI Dealing Certificate (#387)

A bank quotes a spot rate that is verifiably incorrect and deviates substantially from the prevailing market rate.

you should hit the price and hold the bank to the quoted incorrect rate, as the quoted party is entitled to hold the quoting party to an erroneous rate
you should ask the dealer to check his price, as it is highly unethical for one party to hold another to an erroneously agreed rate
you should point out the mistake and split the difference
you should keep on dealing with this bank until the mistake is rectified