You gotta know when to hold 'em and when to fold 'em - a skill this dude clearly lacks.
a deal is a delicate art. You've got to gauge how far you can push the other party - go *too* low and you've ended negotiations before they ever started. Don't go low enough and you've left money on the table.
Then you've gotta consider how willing the other party is to walk away - if they're desperate you've got more leeway to go lower. If they have plenty of other buyers, however, you may need to just pull the trigger before you lose out altogether.