Really depends on the situation. Just the other day I was sitting in the procurement office of a large hotel with my boss trying to get a deal to supply them leather for upholstery. They haggled before a deal/contract was made, what's wrong with that? Although they did try the "can you give 50% percent off" trick haha. However if like someone mentioned above someone is haggling after they've agreed to a contract that is not okay in my opinion.