Andy C is right that you should charge extra for the removal, but that is where the problem can lie, in that the customer would then expect a discount if they keep the wood.
Lets assume its logs not milled wood to keep it simple.
Cut down tree and remove brash 300
remove larger wood also 100. Total job price 400. customer accepts and off you go.
Now you workign away, and you know there is 2-300 quids of logs from this job (once seasoned, split and delivered) and the customers asks to keep it and expects 100 knocked off the bill. If you are there with two trucks ready to take it all, and you are expectign the additional proffit at a later date then it is a difficult situation, but if you knew before hand you could have changed your plans, made it a half day job and booked something else in.
You have to explain to the customer that if the wood was rubbish that you would be charging 200 for the removal of it, but you discounted that to 100 cos you can sell the wood to make up the difference. Therefore you offer to split the difference and charge them an extra 50 to leave it behind. You get 450 and don't move any wood and they get 300 quids worth of wood for 150 but they have to split it.
Never works!
When you say you are planning on sellign it, you can see them think that they should be getting some of the money. I explain that they are already getting it in the form of the discount for removal, but if they want the full money for it then pay mne the extra 50 and sell it themselves. They rarely go fo it.
Customers who are definalty keeping the wood right from the start get a cheaper quote cos we save so much time on those jobs, but discounting the actual work to get the wood is not a great move IMO.