A: I heard this startup is making huge profits.
A：我听说这家初创公司利润丰厚。

B: Be careful, they might be a fly-by-night operation.
B：小心点，他们可能是一家不靠谱的投机公司。

1) 不靠谱的

2) 投机取巧的

3) 昙花一现的

1. 不可靠的，不诚实的

adjective/noun

1. Unreliable and untrustworthy, especially a person or business that is likely to disappear quickly to avoid debts.

Synonym: unreliable, untrustworthy, shady