Here's something that confuses me. Browsing some vendor profiles, I see things like:
Please DON'T use PGP in PM's or e-mails unless the content is sensitive. Use common sense. PGP is for PRIVATE INFO ONLY! Not for chit-chat!
In this case, the vendor is SilkySm00th on Agora, but really it doesn't matter who it is. I use this vendor as an example because their profile page quite explicitly says "USA only", so I could never order from them anyway.
Having been using PGP religiously for over 10 years now, I find it strange that anyone would recommend not using PGP all round. Maybe it's because I'm a touch typer, but I can type my passphrase in about 10 seconds. Since its 50 characters alphanumeric with symbols, the possible argument that it slows things down doesn't really wash with me. Assuming you have a more "normal" passphrase, It'll become familiar over time, and you'll be able to type it quickly before long.
Assuming worst case scenario, that Agora (or whatever market you use) gets seized, and even worse, suppose a weakness in RSA has been discovered, such that an encrypted message can be decrypted in about 24 hours (versus the thousands of years it's currently estimated to take). If all that's encrypted is addresses, then every day the feds can compromise one new buyer. How long before the buyers dry up?
The feds don't know what's encrypted until they've taken the time to decrypt it - so whilst stuff's still encrypted, they can't tell the difference between chit chat and addresses. Decryption time costs the police money. More to decrypt equals more wages to pay someone to do it.
Encrypting absolutely anything and everything is something that, further down the line, stands to help protect buyers, and the effort to the vendor is minimal.
How many other vendors request that buyers don't use PGP for general messages? And it would be nice if such vendors could offer their justifications on this. As a buyer, I'm definitely following the principle of not giving the feds an inch - because they trust me, give an inch, they'll take a mile.
I think this is more a thing for the larger vendors who get tons of messages a day. Having to decrypt general conversation that didn't contain sensitive information could become time consuming in that case.