People forget that humans are just animals (that can sometimes reason and talk). I still stand that dog training guides make better parenting books than many parenting books. At least up till around 3 years old.

The extension of this to adults is more challenging. Intent matters. This could be used abusively VERY easily. That is not happening here, however. With great power, comes great responsibility.

It's also worth noting that, if you use this, plan out how you will explain it later. A panicked, "oh shit, (s)he caught on!" will look bad, no matter what. A calm, thoughtful, positive explanation, delivered with confidence will likely get a lot more acceptance.

A: "Ok, what's with the M&Ms?"

B: "You've noticed then. :)"

A: "..."

B: "I noticed chocolate made you happy. I also noticed you were trying to overcome some negative habits. I decided to help. Whenever you put effort in, I rewarded it with a bit of chocolate. It makes you happy, and helps you lock a good habit in better."

A: "... You've been conditioning me?!?"

B: "Yes, don't you like the improvement?"

A "... yes, but I'm not sure I should..."

B: "M&M?"