How do I estimate candidates' feedback to... you, or to me? Sadly, very few candidates give me any meaningful or actionable feedback after we do cases. Just like everyone else, I progress better if you give me (actionable) feedback, so I wish I would get more. End of rant :)
Assuming you were asking me how I rate candidates' feedback to their fellow candidates now: I frankly don't think it is very good most of the time. At least my own feedback wasn't good back when I was in your shoes. You need to understand something to explain it clearly. If you don't really understand how to do a case, you may say something like "yeah, was good. You should improve your math, and the framework wasn't great, and maybe you should do this or perhaps that...".This is not actionable, and wrong half the time. I am embarassed by some of the feedback I gave way back when!
There is a reason some of you guys are willing to pay hundreds of dollars for good coaching: Our feedback is typically much more pointed, much more actionable.
My recommendation is such: do a (couple of) case(s) with a current/former consultant early on, and write down their feedback; practice on your own and with fellow applicants and work on the initial feedback; mid-way through your prep, perhaps do another case with a consultant to course-correct. Near the end, do one or two more cases w/ a consultant to make last-minute adjustments. All throughout, do 15-20 minutes of mental math and market sizing every day.
Look, I know some of you may think I am just talking my book and trying to convince you to spend money - no, I am not. I was lucky to have 5 friends at BCG when I applied, and each one of them gave me at least 2 cases (for free). But if I had not had these friends and had just studied on my own, odds are I wouldn't have made it, plain and simple. If you are in school, you probably have access to alumni or upper classmen/women who have at least done an internship and would be willing to help for free. If you do cannot find someone to help you, my honest opinion is, get ready to spend some money. Yes you can get in without this - but the odds would be stacked against you. It is a competition, spots are limited - and we always have a lot more qualified applicants than openings. Luck definitely plays a role, but you might as well be as prepared as possible -> At the end of the day, nothing can replace the feedback a current/former consultant can give you.