A Yard Sale Return??

We had a garage sale today and this lady came up to buy some of my girls clothes. She said,"How much?" I said," 50 cents each." She said, "10 cents." I said, "No, 50 cents." She said,"Ok..." She then starts piling up the clothes and I said,"Would you like me to take those for you so you can shop more?" "Sure." She says. So I count her first pile which was 40 items. I say,"That is $20." She says,"Ok." She still shops...Gets more items I make another pile this one has close to 6o items....and so on as she shops. She ends up with over 100 clothing items....So finish counting and I say,"That will be $50." She pays me and I get her a box to put the clothes in. I see her go to her car and she is gone for maybe a few minutes and she comes back and says, "You overcharged me. I wanted it for .10 cents an item." I said, "No ma'am I said 50 cents." She said, "Well then I will return." I said, "This is a yard sale not a store. I am not returning your items." She starts to get mad and walks to her car and brings back the box puts it right in the middle of the driveway and says, " I want you to return it and recount...." I said," I am not returning anything. You already paid me and took the stuff to your car. I am not returning it." At this point she stood there for a few minutes while I ignored her to help other people. She finally picked up her box and left.....

After the fact I should have said,"Well do you have a receipt. I only accept returns with a receipt."

Next sale we will hang hang a sign that says ALL SALES FINAL!!! NO RETURNS!!!