Ask them how much they will discount their traditional commission (just their portion - you want to keep the buyer's agent fully motivated) because you are very close to going the flat fee route. They'll probably balk and turn it back into a question to you (you could always counter with 0.0% as a start), but keep the limbo contest going from agent to agent. Getting listings is critical to most agents, so it's definitely negotiable.
I would also probe their tech savvy with open ended questions. Some are great, use every possible resource, and are very good keeping you up to date via email / text / etc. Some are not.
Be careful in how you ask what they'd list it for, and only consider their answer as a small data point. They're going to be reading you like a book to see if you want it high or realistic. They'll likely opt for the former knowing you're interviewing other agents, so ask them to point out the best comps on the CMA as backup and check out those houses (at least what you can see from the curb and zillow, which may still have history) yourself.
But to bury the lead, you may not need a broker / listing service at all. Set a "make me move" price on zillow and start talking that your house is going to be on the market so everyone knows. Not using a broker has its own perils, but you can use the standard forms and hire an attorney (who'll actually give you real legal advice - brokers can't / won't) if you actually find a buyer who has a similar concept of the house's value and is willing to split the transaction cost savings.