It's not entirely random but, like everything else in the game, there is a very strong random element to it.
I can tell you for the first option it depends on the difference between your intelligence and the intelligence of the interviewer, for the second option it depends on the difference between your interpersonal skills and those of the interviewer and for the third option it depends on your attractiveness combined with the perversion of the interviewer. They also have to actually be interested in you. Also, the difficulty setting matters. Lying on the CV increases the chance of a job interview but not actually getting the job and there's a chance they find out and reject you. Interestingly the salary has no impact on difficulty. Flirting unlocks the options to go on a date and have sex or just have sex there and then. Date then sex gives half the boost to chances of getting the job than just having sex then and there does but both of them have a high likelihood of resulting in you getting the job because they can potentially give way more of a boost than the max that would be needed to get the job. Leading them on = almost guaranteed not to get the job. If they're not interested in you flirting pretty much guarantees you'll not get the job. Just because they're receptive to flirting doesn't mean they want to have sex in which case picking that option means you're pretty much guaranteed not to get the job. The number of times you flirt is a huge factor in the success rate of this route.
To give an indication of how random it is first to get a job interview it basically compares your combined intelligence and interpersonal to a random number, the interviewer is randomly rolled so their intelligence and interpersonal skills can be anything, the difference between your level and theirs is then compared to a random number and then even if you "win" it increases your chances of getting the job by a random amount including 0 though not likely to be. Finally whether or not you actually get the job is done by tallying up your performance during the job interview and again comparing to a random number although this random number can be as low as 0.