Probably can not be of much help as I am in another state. I can give you a basic of what TX requires. I have been doing a particular market for over 20 years, I go for 5 days every month, there are over 5000 vendors there. I have had the same spot all these years. The management is required by the state to have our sales tax permit number on file. Representatives come around every few years just to check to see if we have our permits visible to the public.
In TX you can file for a sales tax permit but that does not mean you ever have to use it.
You probably need to check with you state comptrollers office and see what is required.
Do not let any of this make you nervous, it is all very simple. Even if you are selling your items at a show and you are asked to show your permit all they will do is fill out the paperwork there on the spot and you will have your sales tax permit.
Once again, this is how it is in TX. Hope someone else can reply to your question that is in your state.
Hope you have a great show.