This is a VERY confusing subject for most photographers. I will link to a few important website you should read regarding the collection of tax:
And finally, a fancy PDF with a bunch of handy info:
Basically, you NEED to be collecting sales tax and paying it out to the government. I have several clients who are not required to pay sales tax. Some of them are exempt, because they are charities or schools. Some of them have a state sales and use certificate, and my photos will become part of a product they are going to resell (like a magazine or newspaper). Some clients are out of state and I will be shipping the final product outside of Texas’ borders.
However, other clients I DO collect sales tax on, and I send it in to Austin every January. If I shoot a wedding or family portrait, I am REQUIRED to collect tax. You should be doing it as well. If they can’t fill out a resale certificate form for you, then you have no other choice. They won’t be reselling the wedding album they bought from you. They have to pay tax.
Anyway, the above links will help you get a better idea of when to collect sales tax and what to do with it when you do. Hopefully, this will help make sense of such a confusing topic.