Roughly speaking, the two main ways to sell computers are, and particularly were in the old days,
Three digit price tag sold to individuals => mass market, department stores and suchlike.
Four digit price tag sold to businesses => dealers, who are specialists in computers, provide advice, support et cetera.
Apple and Commodore both had extensive dealer networks in the late seventies. (Commodore ditched theirs when they switched to home computers, and Apple a few decades later went into retail themselves, but that's another story.) So basically starting from 1977, they acquired networks of thousands of dealers very quickly.
Where did the dealers come from? They can't already have been specialists in selling personal computers, because those didn't exist before. Were they in business selling something else previously or what?