arenalife

It all depends on your bike, if it's a old scruff bag, niche model or tasteless modded bike you're better off selling it. Dealers love clean original desirable bikes. They sometimes offer as much as a private sale price for them, they have done for me a couple of times in the past.

As soon as you start looking at a bike they usually get chatty with you and ask what you're riding now, as soon as you tell them they're working out a deal based on it. If you hold out till the end after all your bargaining for extras etc then surprise them with a PX, don't be surprised if they offer you a lower figure. Usually you'd have mentioned the PX while discussing cost. If they're stiffing you they'll usually keep telling you about 'cost to change up' instead of telling you how little they're offering for your bike.

eBay is very good for getting rid of bikes quick for a reasonable amount. Not as much as some private sales but usually more than PX and you know it's going to go so you can plan getting your new bike around it.