How does Google know if the links you have on your site are paid or not, without having it called out as such ("Sponsored Links", etc.) Does placement have anything to do with it (towards the footer, separate from main blogroll). What of the anchor text? If a ticket vendor, for example ticketsellerplace, is buying up 3000 links throughout the interweb with the same anchor text ("ticketsellerplace sells cheap football tickets!!!"), I know that the lack of diversity in those anchor links could possibly penalize the ticketsellerplace... but does Google penalize the every neighbor within that neighborhood, even if that's the only link that looks like it's from a bad neighborhood? Cheers!
I think you answered your own question in the next paragraph. With that statement, your telling google that ticketsellerplace is buying links. All the people at google have to do is, do a search for "is buying links" - with the quotes, then sift through the results. A lot of times, people that buy links will rat out theirselves. The keywords "sponsored links", and links from unrelated pages says a lot. sometimes people will buy links from pages that are popular with no regard to if the content is related to their site. That is also a sign of a bought link. Look up the blog of Matt Cutts. He is an engineer in googles webspam division. He has posted all kinds of stuff on his blog about bought links.