Can you return an item bought at a government auction?

Usually not. Government surplus is sold as-is, and sales are final on GSA Auctions, GovDeals and Public Surplus.

On GovDeals your only remedy for an item that does not match the listing is to negotiate with the selling agency, and there is no general buyer-protection program. PropertyRoom is the exception: you have 10 business days from delivery to request a return authorization for its errors, but items graded Fair or lower and items marked Untested cannot be returned. On GovPlanet, lots with IronClad Assurance can get remediation if they differ materially from the inspection report.

Because returns are so limited, inspect before you bid when you can, and price in what you cannot see.