Transporting some household items to olhao

Hi all, my wife and I are just in the process of redeveloping an old house in Olhao, and starting to think about how to bring some of our possessions over. We won’t be permanent residents, I’ll be on a 60 in 180 deal, but my wife has German citizenship. I’ve tried researching the rules, but still don’t get it! I was advised by ‘Algarve express’ that I would have to pay, on average, 39% of the value of the items in tax. Who sets the value on used items? I have no receipts, it’s mostly old stuff! Does anyone have experience of this?

Thanks a lot