Hi AK - thanks for reaching out and glad to hear that we're providing value out there.
As you might expect, doctoral apps are different in many respects than MBA apps. The SOP can be quite challenging since many schools offer very little guidance. EssaySnark has supported a number of candidates in successful apps to various PhD and other flavors of master's programs over the years and so we can offer some input - but just be really careful about trying to apply advice for MBA apps too directly to a PhD program. As an example: Bschools don't want academic references for the MBA app but they do want them for doctoral. The way you write the SOP needs to be different in certain respects too - you'll want to focus on specifics, in terms of what you have done and how it's prepared you for the PhD program and what you want to do with it, but instead of a professional focus you'll obviously want to position it in terms of academic research and focus areas.
In terms of your question on if you're qualified: Hate to punt on it, but it depends. The good news is that there's a LOT more funding available for doctoral students than there ever will be for MBAs, so that can be an option for a successful applicant (it's not the norm for MBA studies). You'll also have more opportunity for working as a TA or whatever, so there's support available.
But the fact that you didn't do so great in your master's is indeed a concern. You'll need to explain that carefully, and show why it's a non-issue. Since you're applying to such an academically intensive program, the schools will want to know why - especially in light of the not-great performance in grad school.
There's a double-edged sword with these doctoral programs: There's not that many people applying so it's relatively easy to stand out from the crowd - you won't be facing the same issues coming from the oversubscribed candidate pool as you would for an MBA. But the schools only admit a handful of doctoral students each year, so the competition is nearly as tight.
Also just make sure that the GMAT is the right test. We're assuming you've done that research already but the requirements vary widely. Some schools will only accept the GRE; in fact, we usually see GRE as the norm for all types of graduate programs once you move outside the standard MBA. It may be different with marketing analytics / consumer behavior since that's more "MBA-like" than some other academic subjects.
Hope this helps a bit - it is exciting to hear that you're going for this as there's certainly a lot of interest in this area and it's only going to be increasingly popular in the future. The bschools will need you to teach future MBA students on this stuff!!!
Let us know if we can help.