Yui is single-handily the most powerful character and the only reason why she would be so "generous" is so that the person receiving her generosity would automatically turn into her new puppet

You can see this with:

Kousuke

Rand

Alyssa

and to an extent Shin-ae

When a person owes their entire career to Yui, she has more power to find cracks, manipulate and overall find short-cuts towards her ultimate goal. These people who accept her offers have no choice but fulfill Yui's desires in order to keep their dream alive because they probably know Yui has the power to make it vanish.

The only reason why Shin-ae was exposed to the worst of Yui is because of how Shin-ae had virtually no support-system. Also she's poor. Yui thought she could get away with shadier stuff easier with someone like Shin-ae.

Basically dealing with an offer with Yui is like dealing with the devil