Not just selling them things but selling yourself
first.
Before I was a full time programmer I was a salesman when I was young (I'm by nature an introvert so it wasn't anything that was natural, I had to learn to do it and I got good at it - The company I worked for I held the highest sales for the district and the 3rd highest average order value over the company (150ish locations)) and after a while I realised that 'people buy people' with the product often been secondary (turns out all those 'CTO made the choice over a round of golf with <IBM|Oracle"> sales manager' jokes have a basis of truth, they figured it out decades ago).
It's also something of an awkward truth in that as programmers we like to think we pick thinks for objective considered reasons rather than because we like the person pushing them but then I used to watch the tech industry go nuts after a Job's sales event and think..maybe not so much.