Dishonest

I bought a free-range chicken for $7 here in September and paid with a $20 bill. I put the bill into the clerk's hand and told him it was a $20 bill. I received only $3 change. The clerk said that I gave him a $10 bill. I asked him why he didn't say anything when I first told him it was a $20, and he insisted it was a $10 bill. So it cost me $17. I won't go there again.