There are several black chain : hidden links, bulk links, send a lot of spam and buying links. Today I talk about the buying links. Many black hat will perfer to buy government sites and education sites because government and education sites have a great weight ,index fast which will give us a very good effect!!! Then search engine be given great weight to the government and education site import link, is a good investment and extension to your vote, then your station naturally go to good ranking. That is why government sites and education sites are populare to buy and sale link. As we know,government sites and education sites are the most expensive link for sale.If you don't have enought budget,you can not aforrd it. By the way, it also needs a good site to support it for ranking good for a long time.
No doubt government and education site links are most valuable as link juice, but any illegal and back-door link which we can call Black Hat Practice or Black Hat Link is harmful to our site by giving any benefit instead.
I doubt how an individual is eligible to develop government site! - At least Government approval should be needed which I don't think is possible for an individual who is providing advertisement spots on them.