I have bought large groups of tickets on both F9 and NK with only myself present.

Can anyone confirm as to whether miles are earned for tickets purchased at the airport?

I am also an elite member, so advance seat assignments are important as well.

Yes, the ticket is exactly the same as if booked online. You can purchase your seat assignment at the counter if you'd like or you can add it when you get home. I've occasionally also had them add a preferred seat for free when I've asked nicely.

just returned from the airport. (CLE)
I purchased three o/w tickets and saved $19 each.

I gave the counter agent my FF#, and he said he entered it, but he was not able to select free seats for me. (which I am entitled to as an elite member)
I looked at the reservations when I got home and noticed he had entered my name differently than it appears on an existing reservation and in my profile. My FF# was not on the reservation.
I changed the name to match and was able to enter my FF# and select free seat assignments.

My existing profile has no middle initial, and lists "JR" in the last name field, NOT in the suffix field... apparently this all must match exactly.
Capitalization didn't seem to matter.

I'm not sure, but I think the NAME CHANGE must be done within 24 hours of making the reservation.

Keeping track of the CIC
 

Anyone keeping track of the prices? Is this flat and going up or is it a variable number. I'm trying to book NY->ATL for end of August and it is currently $38.

I did the same flight earlier this month and checked my reservations in my email. The price of the actual ticket was more but it seemed the overall reservation was less because the CIC must have been cheaper.

I have purchased about a dozen o/w fares at the airport in the past two months, and the Carrier Interface Charge (CIC) has always been $19. (CLE-LAS & CLE-MCO)

Does anyone know if you can use a travel voucher because of a cancelled flight at the airport to avoid the CIC?

Will Frontier honor sale airfare prices if you purchase in-person at the airport?
Are you able to use cash or credit card?

Edited to add:
Based on another thread, it looks like Frontier won't honor Discount Den prices for airfare purchased in-person at the airport.

Correct.

They will not accept cash at the airport... at least they don't at CLE, but I think you will find it the same everywhere.

$1630 in person at TTN vs $2030 online (7 tickets). Did not present an EarlyReturns number but will try to get credit. Can't beat it.

Promo code
 

When buying tickets the airport. Can the ticket agent enter in a promo code?

Nope.

Bought a ticket at the counter earlier this week. The DEN-LAX airfare portion was $3.72 r/t hah! $32.40 w/ taxes. The ticket agent said she had seen the fares earlier in the morning and bought one herself. She didn't seem to understand why the prices were cheaper at the airport so I explained the CIC. She applauded me for being clever.

She gave me a seat without me asking. It was a window in the way back, I almost certainly would have gotten a better seat if I just waited until checkin. At least it wasn't a middle, then I think I would have been forced to pay to move out to another seat, gah!

$25 "airport fee" for Frontier bookings?
 

I just went to the ticket counter to avoid the CIC fee and they told me that I would have to pay a $25 "airport fee" for any booking! So the $19 fee is waived only for a new $25 fee to be added, so the cost of the ticket was actually $6 more than online. Given that the optional nature of these fees is how the airlines ostensibly avoid paying excise tax, I am not sure how this is legal, since it appears to be impossible to pay SOME fee that is imposed by the carrier. I even called the airline and the lady told me the CIC could only be waived at the airport, but didn't know about an airport fee and said I'd have to go to the ticket counter. Ugh. It's not alot of money but I still feel swindled.