Maupassant writes like a sophisticated fellow who knows the world, and particularly the world of "society" (high society). He's an excellent social observer who's willing to share his insights with his readers, casually throwing off large summary statements like:
..she was unhappy as though kept out of her own class; for women have no caste and no descent, their beauty, their grace, and their charm serving them instead of birth and fortune. Their native keenness, their instinctive elegance, their flexibility of mind, are their only hierarchy; and these make the daughters of the people the equals of the most lofty dames. (2)
You also get the sense that Maupassant is detached from what he describes. Though he understands the society scene, he's not caught up in it, which is why he can describe it so easily. And he seems to know the world of the poor (when the Loisels fall) just as well as that of the middle and upper classes.
Maupassant's descriptions of his characters are an interesting mix of detachment and intimate understanding. He sees into the emotions of Mathilde, his main character, clearly, and can make us as readers feel "inside" her world. But the narrator doesn't share her emotions, and we don't either. That doesn't mean Maupassant seems cold or indifferent to the characters, though. In the few telling moments when he moves beyond detachment, it is to express what looks like sympathy, or even admiration:
Mme. Loisel learned the horrible life of the needy. She made the best of it, moreover, frankly, heroically. The frightful debt must be paid. She would pay it. (98)
Maupassant's detachment also keeps his narration from ever being judgmental, which is remarkable. You might want to judge Mathilde, but Maupassant never does.