@Maxim **********
Not true, there is no single category for all electronics. Laptops and monitors for example have no import duty.
I brought a large computer monitor into Thailand at BKK airport, had it stopped and checked by customs as they thought it was a TV. When they saw it was a computer monitor they let it go, paid nothing.
VAT and duty on shipping might apply if over the de minimus, but certain product categories have no duty on them.
As for Amazon, I just added a Dell XPS 15 to my cart, put in a Thai shipping address, it qualified for free international expedited shipping, the import duties deposit was 7.62% of the laptop price.
No idea why it was more than 7% VAT but nowhere near 20-30% as you claim.
Also, “shipping costs for taxes” isn’t some agreement with Amazon.
Import duties have always included the cost of the item plus the cost of shipping plus the duty percentage based on the HS code of the item plus VAT.