[gowld]

You don't need the agent to close the deal. If the agent peters out after the first hour of negotiations, you can take whatever they put on the table and continue yourself.

Anyway, look at the numbers here: a good salary negotiation takes maybe 5-20hrs to fight for, I don't know, $10K-$50K/yr gain? And a $5-$50k sign-on bonus? Even targeting an "premium consulting" rate of $500/hour, the agent can make a lot of hay to get their cut, putting in the basic standard amount of work.