In the link to Thai Customs ... https://www.customs.go.th/list_strc_simple_neted.php?ini_content=individual_160503_03_160905_01&lang=en&left_menu=menu_individual_submenu_01_160421_01#individual_F01_160426_04
There are 3 categories:
1. Cigarettes and alcohol. Limit is 200 cigs and 1L alcohol. Any more must be put in the bin (you lose it). If you don't put it in the bin you get prosecuted (and lose it)
2. Nothing to declare. Self explanatory.
3. Goods to declare. Anything except cigarettes and alcohol, which are already covered in the first category. I.e. - handbags, watches, perfumes, etc above the 20,000 baht value limit.
If you insist that alcohol can be declared and duties paid at the airport you need to put up a link.