One thing that happened to me you may be able to exploit was a small change. I called to ask to delay the car collection until the day after arrival so I could drink on the flight. Super helpful agent managed to do that and said she’d add a hotel for that first night, which I was OK with. The result of this was a couple of hundred off the price. This was a trip in F to Florida with a 16 day car rental so they maybe had some wriggle room on policy/price.