A small additional demand made after agreement is usually conceded, because the other side will not reopen a settled deal.
Karrass's term. The defence is procedural rather than rhetorical: agree in advance that nothing is settled until everything is, which removes the settled-deal leverage the nibble depends on.
In practice
- A supplier who agrees terms and then asks for the delivery charge to be added usually gets it.
- A candidate who accepts an offer and then asks for an extra week's holiday is rarely refused, because the offer is settled.