Aahaid. Two things. One is that these things give you back your investment. The small JDM hatchbacks are strange things. Same packages have different items installed like Head Units, Steering Controls, Rain Guards/Visors etc etc. So there is no certain consistency as such in some items. Therefore, you could always ask the buyer to pay for additional items (keeping in view depreciation). However, if you are going to sell it to an investor, broker or a plain Jane, then obviously you know the end result.
The second thing is, at the time of selling your vehicle, you could always remove add-ons and sell them separately.
Finally, you and him (seller and buyer) will get what Allah has decided for both of you (I belong to that school of thought).