"AUTO relist" will automatically relist your auction after the initial auction expires. "Repost" is just relisting it manually. BEWARE: Auto-relist could cost you more money IF it relists during a non-sale period or if, say it HAD been a 10-day listing & you really din't want to pay that extra $.40 the next time around--it simply relists exactly the way you had it, exactly the day it ends.