Air Force ratings. Are they guaranteed?

I have read and heard people on the internet and around where I live tell me 2 things about this. I want to join the A.F. to be a Fire Fighter (already a volunteer with FF I, II EVOC II, III Hazmat Ops Aerial Ops and EMT-B). Some tell me you can not be guaranteed a job unless it is a special forces job such as PJ CCT etc. if you p a test. Some tell me hold out on the recruiter till they comply and get it in writing. So which is it? Do I have to make a list from 1-4 jobs i want most to least and then a job category (such as general or mechanical) or do I say its my way (firefighting) or the highway. I really only want to do fire fighting but am open to emergency management and possibly security forces but really my pion is firefighting. Oh ps my ASVAB score is an 82. Thanks