Accesive link building which are based on quantity and on low quality websites isn’t good for SEO reputation and especially for Google. if you need some natural backlinks, try to buy them from popular sites with high page rank, and in small quantity.
Paid links are good for SEO only if they look natural. So
1) buy links from quality resources, not spammy directories
2) use no-follow attributes
3) don’t place or don’t buy links in footer space
4) avoid optimize articles/press-releases
I will stick to contextual links that reduce the chances of spamming, i will keep following main points in my mind
link from relevant site,
unique ip address,
keyword variation in link text
& will be focus on quality and not the quantity of link.