I think a huge tell tends to be flying in on monday and flying out friday. A lot of cheaper tickets require you to spend saturday night at the destination to weed out business travel. Other people mentioned multi-stop routing and odd timing (e.g. biz travel usually won't involve leaving at 3pm on a tuestday). Some of this is obscured by day time flights being more desirable (e.g. no one wants to get up at 3am to make a 6am flight).
The other huge tell is last minute purchases. A lot of business travel ends up being decided on a week or two before the flight so last minute flights tend to cost more even though in some sense the value of the seat declines as the flight approaches. E.g. an empty seat is worth $0 and a pure loss to the airline so they should want to sell those seats before the flight even if they get minimal revenue. For biz travelers, clients often pay for travel expenses so inflated pricing for that flight tomorrow is worth it.