My only nit on your comments is the sales. If he thinks he might be good at sales he should give it a try. At one time I was a design engineer/project manager. The company folded so I rolled into sales with a new employer. The salary increase was immediately 40% excluding bonuses/commission. It's been a long time, but my current base is 3X what I made as a design engineer. Now I am a seasoned sales professional with professional credentials, but if successful he could have a lucrative career so long as his boss isn't a buttplug.
I do agree a sales career as an independent consultant is not worth pursuing. Better to have a base salary which is sustainable plus bonus and/or commissions.
I don't intend to attack, but how old are you and what decade was this? Entry-level sales jobs aren't what they used to be. As one example, my Dad sold auto/home/life insurance for a large insurance company for ~24 years, retiring early in 2009. He had his own office and personal secretary (and additional shared support staff) For the last fifteen years of his career, he earned over $250k/yr. When he started up through the early '90s, a new sales rep earned commission plus a salary based on their prior/career sales. This meant it started with a low salary, but steadily increased as your lifetime sales went up. Commission was always low to start, but was the majority of your income if you did even reasonably well. The company restructured and that salary calculation changed and so did the available territory as well as the manner in which the job took place. What once was done by one well-paid sales rep and 1.5 support staff was now done by six people in cubicles earning starvation wages with very little room for advancement.
Tons of industries have reshaped sales positions this way. Lots of people in cubicles replacing someone in an office. You buy online instead of in-person. You get connected to a customer service rep in Manila reading from a script instead of in the same office as your salesperson. For millennials, this career path sucks unless you are in a small handful of fields that rely on someone skillfully manipulating other people -- mortgage brokers or real estate agents, for example. But if OP was the kind of charismatic
sociopath natural salesman who would do well selling mortgages or houses, he probably wouldn't have posted the query he did.
Also, most entry-level sales positions make you work as an independent contractor with no salary nor benefits these days, because it is cheaper for the business to stay afloat, and there are always enough desperate suckers willing to take the work. Add that sales work doesn't translate as qualified experience in most other fields, and it is worth avoiding.
I grant that there are some sales positions that are different. I believe someone sells upholstery to United Airlines and they probably make a mint. But I don't think those few good sales positions are readily available to the average Joe with little experience and limited connections.