Technically, you do not have to have a representative assist you with your sales tax audit, at least not in California. However, having an experienced and knowledgeable sales tax expert assist you with your audit will help ensure that you are on a more level playing field with the auditor. You want to be sure that you have someone representing you who knows at least as much, and hopefully, more than the auditor knows about how the sales and use tax applies to your operations.