Shippi has my support.
“has content which is relevant to your site.” – Relevancy is the key
“Make sure you use a reputable broker” – Poor judgment can get you in hot water
The list is good as well, no additions from me….
“if you buys 1000's overnight, you might have a problem” Is important.
In short you want to ‘mimic’ an organic linking pattern. People don’t usually get linked back to from completely irrelevant sites and they don’t usually get 1000 IBLs (inbound links) overnight. It’s not a great leap to imagine what potential ‘filters’ are in place to fight SE IBL spamming.
I must say that the entire practice has an inherent risk and I do not stand behind them ‘officially’ as an SEM provider. There are many, many ways of running a Link Building program with far less ‘risk’. Due to the fact I am contractually obligated to my clients, this would fall under ‘at your own risk’ for me and I wouldn’t warrantee the work nor guarantee that it won’t backfire.
That said, done responsibly, it can work just fine. Lol… both sides of the coin for you