fly-by-night
n
(pl fly-by-nights) person who evades financial responsibility, esp debts, by (secretly) leaving; unreliable person 为躲债(偷偷)离去的人; 不可靠的人. adj unreliable or dishonest, esp in financial and business matters 不可靠的; 不诚实的(尤指在财务及商业事务上)
a fly-by-night company 无信誉的公司.