Could someone help here? A friend will come from Phnom Penh and meet me in Bangkok. He needs to buy many construction materials and things. A lot of certain paints that I know nothing about. Perhaps 50-100 liters. He asked me if he would have trouble crossing the border with so many things or whether there is a duty to pay. I said I would assume so but I don't really know. How can I find info out here? I think he needs to buy certain types of acrylic paints and maybe quite a lot of them. He said the brand on sale here isn't on sale there. I offered to help but this is something I have never done in my life before. So if we left the country with 100 litres of paint, would we be stopped or charged something? 

If you are checked; 35% duties (7% if it is for a boat hull) plus 10% vat. 

If your friend buys paint from a Thai manufacturer, then ask for a customs form and certificate of origin that it is Thai. Then the goods are duty exempt in Cambodia, and you only pay the 10% vat. Plus you may be able to purchase without paying the 7% Thai VAT, but that really depends on the experience that the selling company has with export formalities. 

Practically no experience tbh, hence the question.