K so your supposed to put a dialog whenever you have a multiple choice thing. But when you try to write down scripting stuff, it won't work. You can't even put an "if statemnet". So how are you going to make a shop? How do you do anything with a multiple choice?
If you want to use standard (non-dialog) scripting in a dialog, you have to use run-script x and the dialog_request function. Look 'em up in the manual, or do a forum search - there're a couple of threads around that explain them slightly more clearly than the manual.