Part of my job is quoting companies for items that may be used on an ongoing basis. Consumables in consigned stock etc.
I have to give a contract end date detailing when the company I work for will have to re-tender for the entire contract or negotiate the new prices with the customer.
During the quoting phase you can say to the customer "The price of certain parts has gone up since we quoted, we may need to take a look at this again" or something but after we agree and put pen to contract paper, it's locked in.
This is on both sides. The customer can't come back and try to hammer you down on the price.
Or, at least, it hasn't happened to me if we/they can.