Like some people have stated earlier newly mined / minted Bitcoins sell for a slight premium because they have no traces of other transactions and as some people are worried that the Bitcoin they buy have some fraction of a bitcoin with fraudulent activity they buy them directly from some pools for a slight premium. people who do this also usually stash these coins away for a longer period of time so that in the future they can be sure that they won't get into any trouble because some small fraction of their Bitcoin might have had a shady past.