Pretty risky however most of Thailand has places and areas where police are paid not to come in to certain resorts and reggae bars etc due to a lot of corruption. Generally some back packer beaches friendly to that sort of thing and krabi province has some places where its tolerated due to certain arrangements. But either way your taking a risk and if caught and you don't have enough money then you will go to jail and can get as much as 3 years for one Bob marley cigarette.