Gary Eggleston published an excellent list of Tips on How to Avoid Fraud on Collectible Coins
1. A person should save the online photo of the coin he wants to purchase. Many sellers remove the image and the title of the item once a purchase has been made.
2. A person should get the description and the auction information. It should either be e-mailed to the buyer or sent in writing by mail.
3. If there are suspicions regarding an auction, a person should ask for clarification from to the seller. This will avoid misunderstandings and confusion on the part of the buyer.
4. A person has the right to refuse any transaction where he thinks the price given on the coin is too high. One should be aware of the standard price of the specific coin and compare it to the price that was given during the online transaction.
5. A person can ensure that there will be no fraud by asking the seller, before the auction closes, if there is any available escrow assistance for the bidder.