Yes backlinks are one of the most important if not the most important way to get your site ranked on Google. However not all backlinks are the same, some can do more harm than good… Google does not like people ‘manipulating’ their search results, but draws a distinction between high quality and low quality links. 
Fortunately, Google cannot know for sure who has built a link, so it takes some time before a poor quality link results in a decrease in rankings for a site, you will see a short term uplift, that’s why such links may be appealing to website owners, but can lead to fairly big drops once google works out whats going on.. 

We run and operate a number of high performing sites that rank high having done only guest post backlinks. Plus we have clients with over $100k monthly click value from solely guest posts. Guest posts work when done right.

We hand pick sites that we think will have the best impact to rank your site higher. We do this based on experience. Additionally we use high quality content. This is for two reasons;

1) top publishers are picky and care about their audience so would only accept high quality content; and

2) search engines are able to detect the quality of the content and rate the value of the backlinks in that content accordingly.

We are higher priced than some other providers but clients of ours can see on a value perspective we provide more. Ultimately clients care at the end of the day about ranking higher to obtain more visitors and more sales, and doing so in a sustainable way with minimal fuss.