According to industry standards, an offer that’s around 10% less than the list price has a good chance of being accepted by the gallery that listed the work. An offer that’s more than 25% less than the list price is likely to be rejected by the gallery outright, ending negotiation.
All offers are binding, so make sure you’re comfortable with your offer. If the gallery accepts, you’ll be charged for the work so that the gallery can ship it as soon as possible.