I have learned the hard way. One of our sites 98 to 99%% of our links are natural (we never sought them; they were linked naturally by others) but someone working on our SEO team bought a handful and we have been de-indexed since. Our traffic has gone down a lot. Remember, this particular site only has only a handful of bought links out of thousands and yet we are paying the price. Short terms greed can do long lasting damage. YOU SHOULD AVOID BUYING OR PARTICIPATING IN LINK EXCHANGE AT ALL COST.
hmmm... But I think the cause of de-indexed is not for only bought a handful link...according to me the strategy of google has been huge changed but till now "LINK" is so effective for seo...yes, you must check the quality before purchasing or exchanging any link if you submit gust post, article post whatever...there are also a link-up with your site, then? so I think there should be some another cause to bad-effect of your site and you must to find out it.
I agree with you, even i have a very bad experience of buying this stupid links and Google punished my blogs for that.