Legal definition … ‘A person handles stolen goods if (otherwise than in the course of the stealing) knowing or believing them to be stolen goods he dishonestly receives the goods, or dishonestly undertakes or assists in their retention, removal, disposal or realisation by or for the benefit of another person, or if he arranges to do so.’ Theft Act 1968. From my experience, if you pay “fair value” then unlikely to face charges.
If, as someone said above, too good to be true, i.e. obviously ridiculously below value, then perhaps yes. However, in an auction, I believe it would be impossible to prove.