Is it best practice to use different keys for each dark net service I'm using in addition to unique username/password? In other words, does it matter that someone could look at a user on Grams and a user on AB and see that he has the same public key block in his profile?
if you are a vendor I strongly suggest to use the same, the pgp key then proves you are the same person aka the same legit vendor. Same with customer, if you want to build a multi market reputation as customer