This is something new for us too -- and we ultimately found that Paypal had the best rates (2.2% plus 30 cents per transaction) for non-profits, no long contracts or monthly fees for the basic account. They will also send a free smartphone or ipad card reader, for accepting cards at school open houses (or wherever you do sales of sportswear, etc)... They even have their own shopping cart setup, so you just create and sell.
Hi, we have a thread from about a year ago with folks talking about the pros and cons of accepting credit cards and at least one community member had some names of vendors you might want to check out....
Take a look at:http://www.ptotoday.com/boards/35-auctions/155667-credit-cards?limit=6&start=6
We just used SQUARE to take credit cards during our auction and it was totally easy. Someone needed to have an i-phone to use it, but wow - piece of cake.