"His lighter is new and expensive."

Translation: Bricheta lui este nouă și scumpă.

[Deisi92]

What's wrong with „bricheta sa”?

[coto.i]

Nothing wrong. "sa" can be used instead of either "lui" (his) or "ei" (her).

Keep in mind though that because it can be used for both genders, "sa" is ambiguous in a situation where both a man and a woman are present. Whose lighter is bigger? If you answer "Bricheta sa e mai mare." there is no way to know if you refer to his lighter or her lighter.