What the poster above me is saying is that you need to spend hours reading every word on this website or else you may fall into a trap. Nobody treats gift cards the way airbnb treats them.
I just found out their gift card policy the hard way. If you want to use a gift card:
1) You must apply it to your account before starting the booking.
2) You must pay in full at the time of booking. If you pay half up front, Aribnb will not use your remaining gift card balance to pay the rest. Instead they will charge your credit card.
I paid only half up front, and later they tried to charge my credit card when I had sufficient credit balance. After an hour on the phone and multiple escalations, I was able to get my trip canceled and I re-booked, paying the full amount all at once with my gift card.
I spoke with four representatives to try to understand their policy, but none had a reasonable answer as to why this policy exsits.