At least once a week someone shows up to buy a ticket as they are not able to purchase a ticket at the airport. This is a function of the airport and the airlines.
Some airlines just have check-in staff (hire a body) to manage the flow of passengers. No way to ‘purchase’. Other airlines may have the ability to purchase… but only at the top fare possible. No specials on offer for that location.
In many cases we get calls from people who need a ticket, and only have cash or access to an ATM, and want us to deliver the ticket to them at the airport. We do that. Along with those cases we often get customers who are at check-in only to discover their existing ticket is wrong, expired, incorrect, and/or needs to be replaced. The airline quotes them a huge price, they find us online and we sell them the same itinerary etc for a fraction of the price the airline offers. Each situation is unique, but as a general rule it is cheaper to buy away from the airport.