The most important thing if you decided to buy char for adena, not real money (it's banable), is buy char with e-mail and after buy change pwd do char, e-mail, and informatoin to e-mail to changing pwd.
When you buying char from unknow person, you can ask him to write some declaration to your pm, like this: Me ....(nick in game) decided to sell char name ...(nick buying char) with acount, item and e-mail to ... (your nick) for ...kkk adena (or items). If somethig with transaction are wrong I agree for ban my acout by GM.
You make screen shot with this and if something were wrong you send this to GM by ticket to suport.
The person from you are buy char, probably ask you for the same declaration.
Or you buy, or get char form some your friends who don't want to play.
I really doubt such declaration would make any difference. As far as I know buying/selling chars is allowed but not supported anyhow. If you get scammed its ONLY your problem.