Matt Cutts in this video suggests something of a flexible but nevertheless consistent approach to dealing with web spam....
Does Google use a set standard for manually removing webspam?
Google Webmaster Help - March 4, 2013
As Matt describes it, a spammer's history does enter into it. The spam team is sympathetic to situations a webmaster might have inadvertently gotten into, while being much harder on repeat spammers and on exploits "involving malware, hacked sites, or really malicious stuff".