I came across a recent article in the Black Star Rising blog by Jim Pickerell about scammers trying to rip off artists by sending e-mails expressing interest in buying their work. This article struck a familiar chord. In the past six months I have received two solicitiations identical to what Pickerell describes. After I responded with the requirement that payment be made through PayPal, the interested parties disappeared.
Read Pickerell's article. It's short, highly informative, and can save you some grief.