Bait and Switch
Typically, negotiation involves receiving an offer and considering it, not considering something else. The bait and switch is when someone offers one thing and it is switched out for another. This is very deceptive but more common than one would think, especially in the technology business where some are easily dazzled.
“The blue color you ordered was unavailable, so we have this red one for you.”
To combat this tactic, account for offers as presented and inform the offeror of the gaps. Call out the switch. Ask for diminution in value or other serious concessions if the bait is non-existent.