I’m not happy with my part exchange value
The amount a dealer is willing to offer under a part exchange is up to them.
If you are looking for a higher purchase price for your vehicle, you have a couple of other options:
1) Try selling your existing car privately (but that is not practical if you have existing finance on it)
2) Try to negotiate with the dealer and see if they will consider a higher value.
Remember the dealer will be looking to purchase your car at a Trade Price, as they’ll probably have to spend money on the car to bring it up to a sellable standard for them. So, the amount you see comparable cars selling for online is not a true reflection of what a dealer may offer.