When the census taker came asking questions, they didn’t require the respondent to “prove” the answers they gave. They took them at their word. If your relative gave clearly incorrect information, the census taker may have asked someone for clarification. But for the most part, what your relative said was what got written down.
They didn’t ask them to validate those property values in the 1850 or 1860 census. They didn’t ask to verify ages or places of birth. Answers regarding citizenship status and eligibility to vote were taken at face value (for those enumerations that required those details).
Your relative providing information may have guessed where their mother was born on their 1880 census enumeration. They may have guessed about the place of birth for their mother–in-law who lived with them and whose memory was questionable on certain days.
And when asked about the cousin of their husband who moved in ten years ago and never left, they might have said “is there a spot for ‘total freeloader’ on that there census sheet?”