(とりひき) Negotiations – only used in business, where one company is negotiating with another company.   $$$
(こうしょう) When the cops are negotiating with a hostage-taker, this is the word we use. It’s not limited to hostile situations:it also is used in peace-time diplomacy, like trade negotiations or etc.
(ねぎる) Haggling – unlike 取引, 値切る is used in one-on-one interactions, such as bargaining with a store-owner over the price of a head of lettuce.