Used about a company or a businessman you should not trust: they have not been around long, they are only chasing quick money, and they may well disappear before you can complain. It suggests both newness and dishonesty together — a shop that opens, takes deposits, and is gone next month.

Used about用來說 you should not trust你不該信任的 a company or a businessman公司或商人： they他們 have not been around long沒開多久、 they are only chasing只想追 quick money快錢， and而且 before you can complain在你來得及抱怨之前 they may well disappear很可能就消失了。 It suggests它同時暗示 both newness and dishonesty together又新、又不老實—— a shop一間店 that opens開張、 takes deposits收了訂金， and is gone next month下個月人就不見了。

This is a strong criticism, so people use it about others, never about themselves.

This is a strong criticism這是很重的批評， so所以 people use it about others人們拿它說別人， never about themselves從來不說自己。

It goes before the noun: 'a fly-by-night operation', 'fly-by-night dealers', 'some fly-by-night outfit'. The tone is informal and rather scornful, common in news stories about scams and in warnings from older people.

It goes before the noun它放在名詞前面： 'a fly-by-night operation'一個撈了就跑的生意、 'fly-by-night dealers'靠不住的販子、 'some fly-by-night outfit'某個來路不明的小公司。 The tone is informal語氣不正式 and rather scornful而且相當輕蔑， common in news stories about scams常見於講詐騙的新聞報導、 and in warnings from older people和長輩的提醒裡。

The image behind it is someone who leaves in the middle of the night — the way a tenant used to slip away without paying the rent.

The image behind it它背後的畫面 is someone是一個人 who leaves in the middle of the night在半夜裡離開—— the way就像 a tenant used to從前房客 without paying the rent不付房租 slip away偷偷溜走的那個樣子。