Can I trade in my Mr coffee, coffee maker that quit working in three months without a my receipt? I don't have it anymore

I think so. You only get the last markdown price.

Cash at self checkout the day before Thanksgiving

How did you pay for it? If you used a debit card or credit card there's your prove there. Always make a point to try an keep your receipts for 1 year. If you have questions let me know.