“Also, link sellers can get very sloppy. It’s a pain in the butt to review a site for approval; sometimes you just want to approve everything to pad your monthly paid link income.”

I think that everyone is getting sloppy. Many (most?) buyers don’t check where their links are ending up.

Sloppy link buyer: “Here is some money. You have approval to buy me any links on this topic with at least a PageRank of x“.

I also expect Google to err on the side of quality search results (i.e. not on the side of innocent until proven guilty).

I wouldn’t be surprised if they do that. Google needs to make sure that they let people konw that they are being penalized, e.g., in the Google Webmaster Tools. I doubt Google will tell people though.

A site with 100% of backlinks pointed at the root is probably owned by a link manipulator, but again, this signal alone would identify good sites like apple.com or ibm.com as link manipulators.

You combine all the signals - then you start to get an idea of the character of a webmaster - which is really all Google needs to know when deciding how to interpret a shady link.

One detection technique that people seem to be forgetting is this:

1. Look at all the links pointing at xyz.com.
2. Are any of those links obviously paid for? (e.g. listed under “Sponsored Links” or linked from several completely off-topic sites - wedding link on seroundtable, for example)
3. If there’s even one obviously paid links pointing at a site, that categorizes a webmaster as a link buyer.
4. When flipping a coin (e.g. when Google finds a contextual link with laser-targeted anchor text pointing at a site), Google can use that fact to its advantage.

Also, link sellers can get very sloppy. It’s a pain in the butt to review a site for approval; sometimes you just want to approve everything to pad your monthly paid link income. So:

1. Look at all outbound links from site A.
2. What percentage of those links point to sites that are categorized as link buyers? If the percentage is high (more than a few links point to link buyers), then the chance of those links being paid links is high.
3. Look at off-topic links to sites with low authority. An editorial link tends to point to sites with high authority, though not always.
4. Investigate the link profile of those off-topic sites. Are they link buyers? If yes, then the chance of these off-topic links being paid is high.

It’s a guessing game, trial by link analysis, and I’d expect the accuracy rate to never reach 100%, but I also expect Google to err on the side of quality search results (i.e. not on the side of innocent until proven guilty).

Take a look through the inventory of the link selling services’ and notice the high number of “make money online” blogs that are full of paid reviews and text links. Many of them have their affiliate links to text-link sellers right next to a block of paid text links.

It would be hard to know what the exact combination of factors are that Google would use to identify link sellers/buyers without having access to the data in their index.

Eliena Andrews