Am I required to collect sales tax on rental income leased to the fed. gov.

Is there a way to find out if a business has a sales tax permit?

I have been wanting to go to a tax auction for years and I think I understand the process but how do I research the property that is for sale? How do I find a physical location of where it is so I can go look at it and make sure there is an easement onto it?

I am building a basement, living room, bathroom, office. Nothing really complex, no loadbearing walls. I have a permit. My brother in-law is also building a basement with out a permit. I will have to pay more taxes when I am done, correct? What is the advangage of getting the permit.