Posting cash is really risky. Many of the packages of paperwork I get from different countries come ripped at the corners as the post office nose about in there. Oddly they never seem to rip open letters or parcels though. I really don't know if they are checking for something or just looking for things to steal.
Where are you? And what kind of quantities do you want to sell? There might be a better way to do this.
That's why you gotta know about your stuff...
To me this never happened and I did quite some Cash in mail trades. With me being on the sending part or on the receiving part. All of it. Never had anything stolen. First rule would be never trade with suspicious countries, if possible only trade with people in your own country so the mail doesn't have to go over any borders.
Second, use tracking possibilities. That way postmen won't dare to steal it since it could be traced back where it was stolen and they could lose their job...
Third, use safe packing methods so you can't see through the envelope and hide the money in somewhere.
If you take care of these things you should be safe. The real question is where are you from where paperwork packages get ripped open? You are aware that you can send in some serious complains about that and well, also definitely should do that?
