Quick google search led me to
https://igaudit.io/ . I've never used it before, but seems like a fun experiment. Note, it doesn't prove or disprove if followers were bought, it just compares the data of 200 random accounts that follow the instagram account being tested.
Ran it on myself. I've never bought followers, but I've definitely had some obvious bot accounts follow me after hash tagging a city or a keyword. That happens to pretty much every Instagram account out there.

Since you brought up Chocolate

Kook Of the Day has a similar follower amount for comparison, but it also gets a lot more people commenting due to the nature of it.

Then I just got curious (not trying to pick on any brand, just went for what came to my head):











Anyways, you can dig deeper on that site and see more stats and how they determine whether an account is legit or not.
"IG Audit works by examining up to 200 random followers for the input user to estimate the user's follower authenticity. For each follower, our algorithm looks at the statistics above and more, and outputs a score between 0 and 1 (1 being real). We then average those probability scores across all 200 accounts examined to produce the final estimate. Follower reachability is one of the things our algorithm emphasizes - if a follower appears to be inactive or follow a high number of people, they tend to score proportionally lower, because your posts + stories have a much lower chance of actually reaching them. After auditing millions of users, we've also modeled the distributions for each of these statistics for different following sizes, and compare the input user's statistics to the expected values given their follower count."