All addon (and game) settings are stored in your 'World of Warcraft/GAME_VERSION/WTF/' folder. Specifically, TradeSkillMaster stores its settings in a file within the 'WTF -> Account -> ACCNAME -> SavedVariables' folder under _retail_, _classic_, or _classicera_ with the file being named TradeSkillMaster.lua. 

Be sure you have WoW completely closed before messing with these files or else your changes may not have any effect. We cannot provide support for, and do not recommend, making changes or modifications to these files.