Originally Posted by jjbiv

I don't think any airport stations actually have agents employed by Frontier. Even CSRs at DEN are outsourced to a handling company. The outstation agents likely work flights for multiple airlines so your luck may be better at "major" F9 cities like DEN, LAS, MCO, PHL, ATL, etc.
I've never had an issue purchasing a ticket at an airport to depart from any city Frontier serves (as recently as October 6). If this restriction were true, it would be impossible to book multi-city itineraries or even a one-way ticket to arrive at the airport you are purchasing the ticket at. I find it more likely the agents you encountered at the first airport either didn't know how to change the departure city (which is easy to do) or just didn't want to take the time to sell a ticket. I would report this experience to Frontier so they can reinforce proper procedures to their ground handler at this airport if this is a common issue. Your experience at the second airport is more typical and affirms that nothing has changed, at least in my view.