I have seen an user which reputation is "6" and I saw one user up-voted the spam post.
Spam post should not be up-voted!
Up-voting and down-voting spam are both bad actions that just make spam stay around longer. Down-voting and flagging as spam doesn't make the spam go away faster.
Just flag the spam as spam; when the user account accumulates enough spam flags, the user will be blocked from posting further spam, and the account will be identified as spammer network-wide. This means any associated account used on other Stack Exchange sites will not be able to spam too.