On pg 104 of the SOS main rulebook, the description of the Persuade skill also mentions the following (paraphrased)…

“It does not include haggling and deal-making; for that use Broker.”

I imagine that Broker was considered as a skill during the beta stages and eventually dropped. Having said that, a Broker skill would probably have been pretty useful. Now that it doesn't appear to exist in the game what skill should be used for haggling etc?

You are correct, sir. Broker was a skill that was dropped from the game early in the beta testing process. It looks that one reference to it slipped through the later playtesting and editing process.

In the final version of the game, I would suggest using Persuade for most deal-making, although I could see using Bureaucrat in a few cases that involve large bureaucracies.