にけちをつける

find fault with

→ に
phrase Rare #40,010
find fault with Used to criticize or complain about someone or something, often unfairly or unnecessarily. The に marks the target of the criticism.
JA: 人の服装にけちをつけるのは失礼です。
EN: It's rude to find fault with someone's clothing.

人の仕事にけちをつけるのは良くない

It’s not nice to criticize other people’s work, you know?

他人のやることにけちをつけるのは簡単である

It's easy to find fault with what other people do.

どうしてジェイムズいつも奥さんにけちをつけるのか僕には理解できない

I can't understand why James is always criticizing his wife.