Sometimes you just have to punt. To me, this means that, after exhausting all of your resources to find the answer, you may just have to make an educated guess. The law doesn't always provide the answer. It's badly written, the regulations may be vague, or the issue may simply not have been addressed yet in official publications.
So what are you gonna do?
Here's my advice. But please keep in mind that your success will rest on things like the mind of the auditor, your treatment of the auditor, how much money is involved, the level of your documentation, etc.
If you have done your research, and you've looked in the books, on the Web, talked with your lawyer and CPA, even emailed the state, and you're still not comfortable with the information that you've been given, then punt. Do it the way you think you ought, informed by the research you've done. I'm guessing your decision will involve paying less tax. But, keep a record of your research. Print out pages off the web. Photocopy text out of the books. Get letters or emails from your professionals. And keep it all in a punt file.
In two or three years (remember, the audit won't be tomorrow), you'll need to explain the reasoning behind your decision to your friend from the department of revenue. If you've got it all together in your punt file, then it will be something that you can easily, quickly and credibly show to the auditor.
Even if you got it wrong, the auditor may respect your effort to do the right thing and give you a break on interest and penalties...maybe even the entire liability itself. But that will only happen if you've got a good explanation. Which your punt file will give you.
Sales Tax Guy