This certainly is the good point. You can enjoy the coin without remorse as long as you never try to sell it and find out if you overpaid. The super rich don't care if they pay 'too much' to get what they want; the rest of us can be free from this concern if we leave the concerns to our heirs.
OP - It is impossible to learn the truth from one transaction. The axiom is once is a coincidence; twice is a suspicious pattern; three times is a fact. You can learn the truth in their next auction by placing two bids on lesser coins. If both coin in at within 5% of your maximum you will have your answer and can act accordingly.
Agreed, Kyzikene electrum is very cheap right now. Of course, one of the reasons is that it does not hold the same fascination as a coin of Alexander. Ask a non-numismatic friend what he knows about Kyzikos and you might get a reply along the lines of "is that some kind of fruit?" Glad to hear it - we take the issue of shill bidding very seriously - it is an offence under UK law and our software specifically prohibits consignors from bidding on their own coins.