I once asked this question on the PSA forum:
Link. The answer was:
"First rule in doing this is to Not, and mean Ever, accept payment through Paypal. I Only accept High Dollar payments outside of Paypal. There are several ways to do this with your Buyer. Usually on Hi Dollar items there has been contact with me before they ever drop the Hammer and I make it clear what my rules are ahead of time. I have never had a 2K plus Sale without some form of Pre Contact, usually to negotiate on price. When we do come to a deal I usually get a Cashiers check or some type of Certified funds and then still wait a few days and have my Banker contact the Financial clearing house for the transaction and do this even with Repeat Customers. I Never ship anything until I am assured of the item clearing. I have no issue with my Buyers being amiable to this, if it is a Legit Buyer of a Hi Dollar item they should have no problem with this and in fact other than a little anticipation on some of their parts, have never had no problem.
... Also, any and all High Dollar items are Shipped USPS Registered with an Additional Second Signature Delivery Confirmation. Have never had a problem this way. "