Charging for installing PostgreSQL is not the same as charging for PostgreSQL.
Bottom line: you charge for services you provide not for software that other people provide.
That's just really not true. There is nothing that prohibits you from selling Postgresql. I mean, it's not a great business model because you can get it for free, but there's nothing that stops you from doing it.
Quoting Adrian Klaver in this thread from about eight hours ago: "You cannot (legitimately) charge the pharmacist for any part PostgresQL."
That was my thought actually. By legitimate I meant in good conscience as opposed to any comment on the legality
