Screenshoot or print the correspondence and keep until the deal is complete. If buying over the phone use your credit card.
Most of it is just common sense....if you smell a rat, then dont get involved in the first place.
I know that many of the rarer drums in great condition are getting harder to find, and when you see something which you've been looking for shows up for sale, it's very easy to jump in with both feet, but make sure that you dont get stung by always using a credit card. If the seller insists on any other forms of payment which gives you no backup then stay away. The drum your looking for WILL show up at some point.
Thats just my view.