Am I eligible for tax exemption on my furniture and personal belongings as a guardian visa holder in Thailand?

In theory anyone on a non immigrant visa may import used personal items duty free within 6 months of arrival in Thailand. They should allow one item of each for electrical items (TV, radio, microwave, etc). In practice it appears that no one has informed the customs guys of this and on import they will pluck a figure out of the ether based on your bill of lading.

You may get lucky - some have had to pay no import tax or duty, but the chances are slim. My import agent told me it’s best to pay what they ask rather than appeal. You can appeal but generally what happens then is they go through your shipment with a fine tooth comb and invariably the import bill will be higher.