Steve wrote:
How much was the ticket you tried purchasing? Reason I ask is most debit
cards have a daily spending limit on them.

Then the excuse from the TA/airline should be "sorry sir, but the transaction
was declined". And when speaking with a human, they should just mention that
this often happens with debit cards due to lower daily spending limits instead
of stating that they refuse to accept such cards.

As far as merchants who are not honoring debit cards, I'm not sure how smart
their systems are when they try running a card,

Large outfits, especially internet sites which capture your credit card
information can easily apply some logic to validate a vard either by obtaining
list of BINs corresponding to debit cards, or perhaps even by having their own
bank block debit card transactions right away.