Financial talk

i'm sort of new to ebay. and my sister was looking to buy a birthday present. so we bid on a bunch of items...thinking we wouldn't get them all. we go shopping and end up buying the perfect gift. point is we didn't need the iteams anymore. so when i get home we ended up winning a bunch of bids. and i e-mailed all the people that we didn't need to buy the iteams anymore. but one guy emailed me back saying.."you do understand ebay charged me for commission right?" so the point is... can anyone tell me someway to cancel all the bids or "purchases" before anymore problems are caused. and how to help that guy get his money back? thank you so much in advance.