It depends entirely on the mood of the officer. I paid duty on used books, cds and some personal objects given to me as gifts. I paid more than they were worth, but I didn't want to lose them.
One of the boxes had been broken open and a few items were missing. No one accepted responsibility.
I have a Thai friend who lives permanently in USA and has dual nationality. He arrived in Thailand early December and had 14 days free quarantine. He is returning to USA next week after obtaining his "Fit to fly" certificate.
Just don't make a claim. I was insured for 1.5 million. I had surgery for 600K and they paid without any problems. When renewal time came, they simply threw me out as I "was too expensive to have".