When I take instruments in part exchange it is sometimes amazing how dirty the keys and pedals are.
Use a soft damp cloth to really clean the keys, a little detergent in the water is ok. (Do not soak the keyboard!)
Use Brasso on the pedals. You probably don’t realise how tarnished they have become.
If you have a polished ebony finish to your piano you can use colour restorer ( from a car parts shop) to remove any fine scratches.
Did you know that you can reset your Yamaha instrument back to its initial settings? Do this by holding down the top note on the keyboard (or piano),switching the instrument on, keep holding the note down for a few seconds. Your screen will show CLR, backup, initial setting or similar. Remember this may erase something you have recorded if you have not saved it.
Of course if you don’t want to clean your instrument, I will still take it in part exchange for a lovely, clean, brand spanking new one!