Joe-job
A joe-job is a message that looks like spam, which is send to damage the reputation of a web-site, by making it look like the message was sent by the victim, who is the target of the spam, not the sender. See: http://en.wikipedia.org/wiki/Joe-job
It is not always easy to see if a spam-campaign is a joe-job, because sometimes one illegal domain will use a joe-job against another illegal domain. So we cannot just decide by the nature of the domain, if the spam that has its name in it, is a joe-job or not.
Have a look at the WHOIS-information of the domain and at its reputation. Check the reputation with a tool like http://www.urlvoid.com . If a domain has existed for several years, and has not been blacklisted, than it is not likely that it suddenly will start spamming.
The style of the spam message will be different from average spam. Real spam will often use redirects and other tricks to make reporting more difficult. Joe-jobs will display the name of the domain in a prominent way, to make reporting as easy as possible. The joe-jobs will also often contain provoking text to irritate anti-spammers. That text can be vulgar words or ridiculous offers like heroin or Tomahawk-rockets. Sometimes this will even be a message as unlikely as “we will send more spam”.
It is important to realize, that the purpose of joe-jobs is, to make as many anti-spammers as possible, submit bad comments and ratings at SiteAdvisor and WoT, and report the spam to services like SpamCop and to Registrars. This means that the spammers use anti-spammers to do the job they get paid for: damaging or even closing the targeted domain. When reporting joe-jobs to SpamCop, only submit the full headers + from the body only the part above any link to websites, and add the text "<truncated>".
As always you should comment and rate a domain according to your own experience. No matter how much you may dislike a certain kind of domain, only comment/rate it for good reasons. The fact that a joe-job has made you aware of the existence of a domain is not a good reason for rating it or commenting on it. Do not let yourself be used by spammers!