Honestly, it's going to depend on the salesman and the sales manager. We went looking for a new van last November after #3 was born. We were indifferent to the Sienna and Odyssey, and were going to go with whatever we could get a good deal on...be it new or used. We tried to negotiate a few different vans and they weren't willing to come down much at all.
My wife found a 2017 Odyssey EX-L with 15k miles at a local Toyota dealership (Tejas) that was stickered at $36k, so I sent them an email asking about it. They replied and gave me a price of $33k. We decided to go take a look at it and see if they would be willing to go down anymore. We test drove it and it ran perfect and looked perfect (no dings, dents, etc). The wife liked it and it had the rear entertainment system that we didn't have to have but knew the kids would like it. Just to take a shot, I offered them $28k (IIRC), which was about what we saw 2015 models with 60k+ miles were being priced at, and they countered with $31k. I made a final offer of $29k, which they rejected, so I shook their hand and started to leave. Before I could get to my car, the salesman was running after me to accept the offer. Considering the soon to be left over '18s with the same trim were in the high-40's and they weren't coming down on those, and some a year or two older with more miles we looked at were priced there and not budging, I feel like we got a good deal. I think it came down to finding the right sales manager at the right time.
The key is something that people here have echoed for a while. Don't get emotionally attached to it and be willing to walk away. You have to manage your expectations about what you think is a fair price for the vehicle and be willing to stick with it. Also, don't be afraid to start of lower than you feel is comfortable. All they can say is "no" and you're right were you started. But keep it reasonable so they know you're serious.
