腹黒い

1. Origins, structure, and basic meaning

• Structure: 腹黒い, read はらぐろい, is an i-adjective for a scheming or deceitful character hidden behind appearances.
• Basic usage: 実は腹黒い reveals a fictional merchant's nature; 腹黒い人物だ is a judgment the source says needs evidence.

2. Common pitfalls and similar expressions

• Hidden motive and evidential caution
  • The second context explicitly says evidence is insufficient, so the adjective should not be assigned to a person merely from appearance.