So you have a competitor who's pissing you off because she's in the number one position and just won't share the guitar and let someone else sing. You pick at the site, you know it's spammy, but can't find anything to nail them against the wall with. Yet you know they're spammy... What do you do? Call an Internet Hitman to take down the site for you?
The Black Glove WebmasterOr would you put on the black gloves and do it yourself? You can set up a network of sites and feed links to them in the spammiest way you can think of (blogs, forum sigs, guestbooks, FFA's, link exchange clubs), then create hallways that lead to more hallways full of hundreds of different anchor text combinations all pointing at your competitor's site.
Next step is to talk about it in the blogs. Say something like, "I was researching the backlinks of a client's competitor, and look what I found!"
Is that an unlikely scenario? Not really. I know for a fact that DDOS attacks have been carried out against websites for the purpose of retribution. Were these attacks done by hire? It is entirely possible to carry out an "website assasination," to "murder a website" and make it go away. It's the online equivalent of setting a competitor's store on fire.
That is the danger in posts like this one from Threadwatch:
FT.com Caught Selling Hidden Links 
In the above thread, a blog is referenced where the blogger recounts how he discovered a competitor of a client (named as debtcounsellors.co.uk or maybe it's debts.net, I'll leave you to untangle that one) had allegedley purchased hidden links on another, quite prestigious website.
Stories like the above make for a funny read. It's like your favorite celebrity caught acting like a regular punter. We all enjoy seeing others exposed, that's why tabloids sell. But I find this kind of reporting to be troublesome because it opens the door for creative assasination.
Would people do such things? Taking a look at what people do to each other offline, hitmen for websites doesn't appear that far-fetched. The black glove webmaster may be the next niche for the unscrupulous. Look for hits to become more creative.