Will one with record of unfinished PhD on his/her CV be doubted of his/her ability?

does a record of an unfinished PhD program makes employers doubt a person's ability?

I very much wish it were not so, but the honest answer is yes. Employers, within the restricted context of reviewing job applications, are forced to rely on very partial and superficial information given to them in CVs and job applications. Moreover, they are given huge numbers of applications to select from under time pressure. They respond to this in a way that I think is completely rational, but nonetheless extremely frustrating (to them as well as to the candidates), which is to assign a highly inflated significance to each piece of information given to them: positive things appear much more positive than they should, and negative things appear much more negative than they should.

In particular, both an unfinished PhD and a long period of seeming inactivity in one's CV are likely to be perceived at least somewhat negatively, certainly if they are unaccompanied by an explanation, and possibly (to a smaller extent) even when an explanation is provided. It wouldn't kill someone's chances of getting a job, and can be overcome by many other positive things one has to say about themselves, but I'm pretty sure it will have at least a small negative effect.

There are many reasons that people do not finish doctoral programs other than incompetence or lack of motivation. For instance, one may become disenchanted with the soft deadlines of academia and would like to work in a non-academic setting, where deadlines and tasks may be completed in a more timely manner. Also, one may like the income security that a non-academic salary may provide, rather than having to chase after grants for summer pay. Yet another example is that one may like fixed hours in their employment, rather than spend evenings, weekends and sometimes holidays working on manuscripts or grading papers. So, it would be advisable to include the doctoral studies to demonstrate graduate training (especially if it is in the area of the non-academic jobs one would apply for) and give a reasonable and respectable explanation for leaving academia. I often suggest to non-academic job candidates in this position to write their reasons for leaving academia in their cover letter so that there aren't any unanswered questions that may damage their ability to even getting to the interview.

For an industry job, I don't think it is a big problem (unless it is a research position where PhD is required).

It is very likely that the candidate found out that he/she does not like to do research, and it might have taken them a while, like it took me.

Of course, I have no idea of what kind of opportunities I would have had if "PhD" in my resume did not have "abd" next to it, but from questions that I had about it and amount of time interviewers spend on those question (if they asked at all) it seemed like a fairly minor point. My previous experience and technical skills get much, much more attention.

And just to be clear I started my first job, while I was still in the PhD program.

I do believe that it is a negative, but a small one, so if your friend does not have passion for research, they should get out, ideally get a job first and then get out.

Also, they should put PhD experience on the resume, being part of PhD program is a plus, this is a lot better than having unexplained gap.