I don't think there's a set career path for those folks, they're just GA or corporate pilots who get into sales. Salesmen/brokers can actually do demo flights with just a PPL, but I'm pretty sure you'd want at least a commercial for insurance purposes. That's for light GA airplanes.

For bizjets, you'd probably need some sort of bizjet flight experience and type rating(s).

I think the best way to approach that sort of career would be do the usual general aviation / corporate aviation career path until you get some bizjet PIC and then look into sales. Piston CFI experience would probably be enough if you just want to do light GA aircraft sales.

You also need natural sales skills (people skills).