I've had good luck on ebay too. Things like an extra data cable for under $3, HDMI for under $6, car mount for under $6 and finally an OEM Sprint car charger for under $10 (oh yeah! I think it's best to go with OEM for chargers
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As for testing a SD Card I would copy about 30g worth of files to the card and then try to read the files, if you can read them you should be worry free going forward IMO.