How much do Facebook Credits cost when purchased with a Facebook gift card?
When using a credit card, credits are $0.10 apiece. When paying via phone they're significantly more. I can't find anything on the PoS display, card, or Facebook web site to find out what the purchase rate is for gift cards purchased in a retail store.
Using the Facebook Credits Gift Card to purchase FB Credits is 100% identical to using a Credit card or Paypal to purchase Credits. You receive the face value of the card in Credits ($0.10 apiece). There are no added fees or reduction of Credits to pay for the costs of this sales channel as Facebook covers those costs as a cost of doing business to provide consumers the cards.