I've said it before, but it bears repeating .... get, and read, the book "What the IRS Doesn't Want You to know." The book does an excellent job of explaining exactly how the IRS is structured, the duties of the various divisions, and the 'mechanics' of audits. Anyone who pays taxes ought to read this book.
A few other observations:
1) It's better for you to meet them at their office. Nothing good can come from them visiting you;
2) Meeting with auditors is what you pay your CPA for. If you don't have one, get one;
3) There is NEVER a 'routine' action by law enforcement that you have 'nothing to worry about.' They're pros ... and in their field, you're a novice. Get your own pro; and,
4) Finally, you have two basic options when dealing with such functionaries: say nothing, or complete disclosure. Lies and half-truths have a habit of biting you. Indeed, this has become a favorite of law enforcement these days: when the original investigation doesn't pan out, lock the target up for fibbing. That's what sent Martha Stewart to jail.