"She wouldn't take my rocks"

Today at lunch, Ethan recounted what we think is a true story (he’s both told us that it is true, and he recounted the same story without much variation to Austin early this morning). I’ll just let him tell it:
“Yesterday, I went to the small store by our house to buy some special treats. But I didn’t have any coins. So I gave the lady my special rocks. She looked at my rocks and said, ‘This isn’t money, its rocks.’ So she didn’t let me buy the cookies.”
The shopkeepers already call Ethan by name (Elhom, his local given name as the “th” is hard for them to say.) So I’m sure the story is circulating of the foreign blond haired boy who tries to buy cookies with rocks!