It’s a real problem. I was suckered into one of these, did 2 long interviews in person and a phone interview. Then after the 3rd interview they said ‘The CFO changed his mind and we’re not going to have this position at all’.
Really pissed me off for wasting so much time and gas.
Typically, I start with (and have gone through, myself)
Phone Interview. Screens out the real bad ones....usually.
On site Interview.
Then the decision is made.
For high-level jobs (Director or higher), or if a key person wasn't available, there might be a "final round".
A request for a 3rd interview would set off some warning bells.
I have talked to HR people who tell me that they advertise and interview for job openings that do not exist because it makes it look like they are doing something.