Trending @Cognizant; I use fake compliments to motivate freshers to do my work. Is that a bad thing?

I've been reading through this group, and it got me thinking about a situation at work that I’m starting to question. Let me explain.

There's one guy on my team who is pretty lazy, almost to the point of being unmotivated. But I figured out that if I compliment him on his work (his work is meh), he becomes attentive and starts really working hard. Same with others: I complimented this fresher for their coding, and suddenly they’re working hard up without me asking.

This actually works and I am able to get more work done.

It’s not manipulative right?

Last week, a couple of freshers overheard me talking to another colleague about how I use compliments to get results. Now they’re acting cold towards me, and I'm getting the sense they feel manipulated.

What should I do?