I use an auto broker for many of my vehicle purchases. The first time I used this guy was for my brand new '07 Nissan Titan. It was a very good experience. I received a price that was better than I could have negotiated.
I'm currently working to buy a 2019 Leaf SV Plus with the weather and tech packages, plus floor mats and mud guards. His discount off of MSRP (42,500) is only about $300, which is very unusual. It's the worst discount I've seen him get. Normally my price is invoice + $300. The rebates (Nissan, Fed and Colorado) add up to around $13K.
For my F-350, I didn't use the auto broker because I used the Ford X-Plan pricing which was below invoice and better than the auto broker could get.
If you're a lousy negotiator, consider using the Costco buying program.
2019 Leaf SV+ with Tech and Weather packages
2015 Leaf S (Totaled 10/2019)
2017 Ford F-350 CCLB 6.7L SRW 4x4