Mom test for hiring marketing interns

Yes I'm thinking of hiring a marketing intern for my startup. I know the dangers and risks. Especially given that it will be a paid one. However, I believe in taking chances. Most full time employees are not great either.. problem with hiring anyone in an early stage is a rather simple one.. most employees look for job to live a good life. Very rarely would you find someone genuinely interested in helping your startup survive, let alone grow. Back to the point, I'm going to evaluate a few candidates. Turns out even graduated folks are applying. Now comes the difficult part. How do I evaluate their motivation? I'm promoting the job post to get a hell lot of candidates. And I plan to interview some 20-50 of them. That's a lot of time but could get me some good ROI.. if I find the right guy The job will be mostly in sales.. going door to door to market our product. I mean emailing, calling, then setting up meeting etc. What kind of questions could help me identify the right person? If only I had a Donna (Suits tv series) to wink at me from the waiting room. To signal that this is a different guy, a Mike Ross (would actually love to hire someone with fake degrees but street smart... Degrees from ivy leagues and work experience don't really help) Makes things difficult.. makes me wonder if there are better ways to evaluate their motivation. Some candidates send linked in invites after their application, which I take as signal of high interest. But that might be pretty naive. Sightly better, 'easy apply' are 'easy ignore'. Only those who email a cover letter or do make extra efforts are worth any time. Do great startups have some proven techniques? After all hiring is an important skill for successful founders. Motivation letters are pretty useless.. filled with standard phrases, no real content. Some sort of mom test could work here? PS: this is pretty usual Reddit thing to mock anyone asking for advice. One out of ten comments are helpful nevertheless.. the rest 90 pc mocking the author worthless