You need the full name & passport to be able to book a flight though. I'm not sure how the agencies can re-sell the flights later on? I'm assuming agencies do

You need the full name & passport to be able to book a flight though. I'm not sure how the agencies can re-sell the flights later on? I'm assuming agencies do that to lock the prices early on for the flights that they know will be fully booked. If airlines didn't do the nasty tricks with the prices changing every minute, this approach wouldn't work, though.