com/topic/seat-of-the-pants-by-the seat-of-the-pants operation but that may be not dishonest enough for your context:-) Perhaps dubious/sleazy operation
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ClivePerhaps a 'fly-by-night' business. 'Fly' here means to flee, to run away. They take your money, and run away secretly and unexpectedly.The term has some "seniority"