Some people hear “no” as an opening offer. Make yours the final price.

For certain people a refusal is where the conversation starts. They push, not usually out of malice, but because in their experience a refusal has give in it, and they are checking. If yours moves when they push, they learn something about you that shapes every ask after this one. Consistency is what makes a refusal function at all.

When the push comes, repeat the same sentence and resist adding a reason. New reasons read as negotiation, since each one is something they can work on. One flat repetition usually ends it, and it costs far less than the fourth round would.