I advertised a California King mattress set on Craigslist. I was asking $900 and the lady asked me if I would come down in price. I did. I dropped it by 200.00. She and her husband came to pick it up and after they got it home, she says she measured it and says it is not a California King that it is a King. I have the original receit and it states the purchase was a California King. Now she is asking for a full refund since she says I falsely advertised the wrong size. Wouldn't that have been her responsibility to measure it when she came to pick it up? She never asked me for measurements. What do you suggest?

She bought it, show owns it. You have the original receipt stating the correct size. Yes, she should have measured before she took it.

Keep your receipt. Most likely buyers remorse or some other con to try and get a refund.

Tell her no, and don't talk to her again about it.