I have never lost a package that was actually mailed, though I have been scammed a couple of times by vendors who never send anything.
I try to stick to domestic vendors to avoid customs, but sometimes it is impossible due to supply issues. When I am ordering internationally I stick to Canada if possible. I once had a package from India get stuck in customs for over a month. When it finally arrived it had been opened and retaped shut. However, they did not find the actual contents of the package, it was very well hidden.
I am not familiar with Clenbuterol but I did manage to buy some Provigil after reading this article (http://www.huffingtonpost.com/johann-hari/my-experiment-with...).
You've said this a couple times - how do you differentiate?
Do you have purchases sent directly to your home/business, or do you attempt to obfuscate the delivery somehow? If so, can you share anything about the tactics you use?
What percentage of your purchases arrive as expected? Do you have any reason to believe that anything is being intercepted by Customs / Border Police / Whatever, or do you only buy from in-country sellers?
Also, have you happened to notice if SR sellers sell things like Clenbuterol, and others that could fall into the "Performance Enhancing Drug" category?