potential client, wondering why i don't answer any of his messages or calls: "I hope I haven't done anything wrong!?"

yeah dude, continually calling me MULTIPLE times after 5PM on friday (second friday in a row) is one way to "do something wrong"

these "business" types know no bounds

charge them more money than you would to normal clients. There, problem solved.

Two numbers.

One to contact you in work hours, gets switched off automatically after hours.

Another to contact you outside of work hours, to contracted customers only, and the contract specifies a call fee which is waived only in the condition it's a critical production issue that's solely your fault.