Using escrow is the finest solution if you feel you are trading with a scammer.
The OP was receiving was receiving messages to conduct business on various websites so escrow would not really be possible in those cases. If you are dealing with a website then you kinda need to deal directly with the site. This is one thing that makes doing business outside the forum dangerous.
As mentioned above all the suggested sites are probably not sites that you want to do business on, at least if you don't want to get your money stolen.