I had been to Chichen Itza and Tulum in Mexico many, many times and had done quite a bit of research (I love me my history!).
Every time I'd gone, it has been with someone who hadn't been before (Mom one year, Dad another, various SO) and they had insisted on having a tour guide. Every time we went, I had to correct the tour guides who would try to dumb it down or make up incredible stories that were completely and wildly inaccurate about what happened where and when.
I'd love to have skipped out on these tours, but was never able to.
BTW - I wasn't sucky about it, just stated that it wasn't accurate and what actually happened.