How can i be sure that my female rabbit has never been exposed to a male?

she is ripping out fur and doing (strange) if you know what i mean things to my other rabbit. at the store the lady said they were both female. i'm not so sure if she's lying because she was trying to convince us to bring home a boy too. my bunny is digging a hole in the ground too! does this mean what i think it means? please some one give me an answer.