I advise my sellers to request that a pre-qual letter accompany any offers. This helps add a level of security to the transaction, at least we know how qualified the buyer may be. If they qualify for a higher price than your home is listed for, the chance for problems is much less.
It is also important to know how much of a down payment they are planning to put down. Though many 100% financing deals go through with no problems, the larger the down payment, the easier the loan will go through.
I personally contact the buyer's lender to see how qualified they are. Though they can't give me some details, they can at least give me an idea on their financial ability.