I would like to add few more points..

1. Be extra careful about orders from Suspecious countries and countries having high risk/fraud rate.
2. Don't enable automatic account approval. It should pass atleast a manual check before account activated.
3. Insist on paypal pay as much as possible. Credit card frauds causes double loss (fees returns + charge backs)
4. Call and verify the request. Our experience says this is the best way to avoid frauds in the begning.
5. Spammers are as dangerous as frauds. So if it is possible, keep as eye for around 5-8 days on new active accounts.
6. Maintain a list of Spammers + frauds information with their email ids, IPs and pattern, as you get information about them.

Hope this will help members in reducing frauds/abuse to their services