I’m looking at booking Turkish air Detroit to Cairo on my own as it appears much cheaper than what the cruise line will charge. But the flights show 3 levels “promo”, semi-flex and flex (almost double the semi flex). I’m looking at business fares. What do most folks book?
The price differential refers to how flexible you want your ticket to be. The most expensive tickets are the most flexible which often feature last minute changes or cancellations with no fee incurred.
I've only flown business with Turkish and always book the standard fare as it's the one that suits my requirements. I generally don't need to change or cancel my flight once it's booked so there's no reason for me to opt for the more expensive flexible option however some people have different requirements.
Scroll down this page for an explanation from Turkish Airlines
https://www.turkishairlines.com/en-gb/any-questions/fare-rules/