Question – Hello, I am a Green card holder living in Texas.  I would like to start sell my handmade craft (cute necklaces) in convention events. (and trying on Etsy). 
It is only me making and only me selling them. I have been asked by ANIME-CON to show a “Tax Certificate Number”, So how do I get one? How much will it cost? 
Maybe I will do it once or twice a year (and hope to find part-time job for the rest of the year).

Our Answer – In order to get the “Tax Certificate Number” you will need to visit the Texas Comptroller to get a Sales Tax Permit which allows you to collect sales tax for the retail items you sell.  There is no cost to obtain the number. 

Here is more information about how to get a sales tax number in Texas.