Junior sales will say yes to whatever the client says they want; Junior engineer will try to implement whatever the client says they want, say no if it's impossible.

Senior sales will try to figure out the real reason of a client's request, and sell them a solution that solves their real problem; Senior engineer will try to figure out the real reason of a client's request, and propose a solution that solves their real problem.

A sales person and an engineer may start from opposite directions, but really good ones think the same.