I touched on this in some other replies, but basically, I use my real name/address, try to use domestic sellers as much as possible, and have never lost a package to USPS/customs.
There are still scammers on SR, but the forums and reputation system go a good job at reducing that risk substantially (edit: if you're smart about doing your research and only dealing with the top vendors).
I do have to meet with RL dealers from time to time, and I vastly prefer SR.
I am not a dealer. As the OP said, I have a gigantic drug habit.
I suspect that, like many HN readers, I am a young guy who works in technology and makes more money than is good for him. I am single and unattached, so I've got plenty of disposable income. And I seem to be good (so far) at remaining a stable, productive employee despite my habit.
As I just mentioned in other comments, I have the packages shipped to my home, using my real name. I have never had a package intercepted.
I think I benefit from the fact that the items I am ordering are very small and fit into normal sized envelopes. From what I've read, packages are much more suspect than envelopes.
I have purchases sent to my home, most of the time.
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 purchase mostly opiates, though I have occasionally purchased other classes of drugs as well.
I have been scammed a couple of times, but I have never lost a package that was actually sent by the vendor. I have a 100% delivery rate.
Every time I was scammed was the result of finalizing early. This is bypassing the escrow system and giving the vendor the money immediately. Usually new users are asked to do this, and some vendors require it. I've learned my lesson and never FE (finalize early) now.
You can find non psychoactive/psychiatric drugs, it just varies a lot and you need to keep your eyes open. Certainly the market for what you are looking for is smaller, but it is there if you are persistant about it.