I applied via email to be a freelance contributor. It took about a week to get the application process started.
Interview
There was no formal interview. I sent my resume and portfolio link. The editorial director then contacted me and provided me with a sample summary and a set of guidelines for creating my own sample. This sample was to be paid ($700) only if it passed an internal review. Otherwise, it was to be paid a $50 kill fee. $700 is well below market rate in my experience. Typically, I would be very suspicious of such an arrangement, but the company was vouched for by a friend, so I agreed. I have spent my career working on highly technical material and so assumed that summarizing the dregs of the publishing industry (self-help) would present no great challenge.
I completed the sample on time, and within the specifications. There were a handful of minor errors, as one would expect for a first draft. These would have been easily corrected. I summarized the book clearly and concisely and used a wide variety of illuminating sources from the psychological and sociological literature to supplement my analysis . I was nonetheless told that the piece failed an internal review and that Instaread did not share the justification for rejection with applicants. When I pressed for a fuller explanation, the editorial director cited a few very minor errors.
Aside from the fact that I find it unlikely that the piece was actually so deficient that it could not be published, it is worth mentioning that this type of unrealistic editing test, which took me some 30 hours to complete, is increasingly under fire in the industry. It places an undue burden on freelancers and, especially in light of the lack of payment, is in my view ethically suspect. Reputable publishers are normally willing to pay applicants for their time if they are submitting to high-input auditions such as the one required by Instaread.
Check out the Columbia Journalism Review's excellent analysis of this issue by Googling Columbia Journalism Review; editing tests.
If you are going to ask for a high-input audition, you should be willing to pay for it. A $50 kill fee for 30 hours of work does not cut it. Not paying for that work is extremely disrespectful of your applicants' time. If you're concerned about paying for low-quality work, take the time to read your applicants' portfolios and get a real sense of what they can do before agreeing to pay for a sample. There are dozens of possible ways that you could set up your interview process in a fashion that does not unfairly disadvantage your applicants, many of whom freelance full time. You should consider doing so.
And lose the attitude. Your business is targeted toward people who are too lazy to read self-help books in full.