If I am going to buy a top dollar value ancient, I only deal with a dealer that has a good international reputation. I have to expect to pay more for such expertise. I keep all such purchase information for such; some of the paperwork for significant ancients in my collection is now over 30 years old.
At least that way, I can vouch for the bona fides of the aureii and the gold stater that I have, and my kids can submit them for international public auction with confidence, if I kick the bucket.