Hi Geoff,
It’s the same as buying privately I think. Some people have had good success with discounts, some haven’t. I didn’t get anything off my Volvo but some did on the same car. I think your geography has a part to play, and whether you’re dealing with a small dealership or one of the monster conglomerates. Also, I’m sure the car choice will matter too. Some dealers advertise discounts, either direct through their websites or via third party websites like Motaclarity. Certainly it seems like it’s worth asking, and shopping around if you have more than one dealer close enough. There is a sticky link on this forum where people post deals they’ve found. Good luck with your deal hunting!
And yes, they’ll take a trade in and return any funds to you as a bank transfer or cheque, or at least mine did. Just make sure, as you would normally, that the price you’re getting is a fair one.