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If I’m reading the question correctly, you are looking to use a reader to read the magnetic stips on customer loyalty cards that you will create and provide to your customers. There is not a widely known company that provides these services in the way Square does for credit cards, but there are a few options. UniMag Pro is one choice for card readers of this type (http://www.idtechproducts.com/products/mobile-readers/126.html).
To create the loyatly cards, you are also going to need to invest in a card writer (http://www.idtechproducts.com/products/swipe-readerwriters.html).
Lastly, you will also need software for your tablet that will allow the reader to work with loyalty cards. The UniScan application is available on Google Play ( https://play.google.com/store/apps/details?id=net.idscan.android.uniscan... ) and should meet that need for you, although you will need to specifically check for compatibility with the model of tablet that you intend to use. BTW, I don’t have any connection with ID Tech products, they just happened to have both Galaxy compatible readers and card writers. Hope this helps.