Hi Andy
I don`t think you have to be too precise about second hand items, especially small ones. Years ago when we brought over a van full of our stuff I was terribly precise after reading the instructions about supplying an inventory. even down to listing childhood teddy bears I hadn¨t been able to bring myself to part with! This certainly caused a few winks and nudges ans sniggers in the customs office in Santander! MY list was so detailed that they took an age to process it and in the end, we had to stay overnight there. The Spanish are not nit pickers in the same way as administrative staff in the UK can be. Don´t get too uptight about the process and put a round price on books and nick knacks.
Good Luck.¨