Its the old black hat manipulation mistake. Many SEO companies will create spammy links on blog networks or with poor quality content. A focus on backlinks, and poor quality private blog networks means you must spend a lot of efforts both in time and money at the expense of high quality content on your own site.
When I stopped even thinking about backlinks as such and more about high quality content on my own site, not only does it take less effort, cost less but the results are there long term. Plus high quality content can actually attract links.
To give you some tips how to do white hat seo. You "may" have several types of content on your site:
1. Converting pages - these are your keywords for your products. You will do good on-page SEO and try to rank in Google.
2. Pages designed to attract links - These are your high quality articles that do not try and promote your products, but instead try to be fun, helpful. They may or may not rank for a keyword (i.e. you may just aim for social sharing).
3. Authority Pages - These may be related to your products that you try to rank for certain keywords, i.e. tutorials, guides, related information etc. These may not attract links, but they may rank in Google. You may use these to increase traffic to your site, but also feed traffic to your converting pages as well as increase the sites overall authority in the topic area. You will also want to link well internally to your type 1 pages to increase the type 1 pages ranking over time.
Now, the really high quality pages (item 2 above) you will want spend a lot of time on, making it look good, be helpful (tutorials are great for this) and as a rule don't try and promote your products. You will place a few subtle links to feed link juice to your converting keyword pages to increase rankings of your converting pages in step 1 above.
This is just one example where you think about your content, site structure, and realize that white hat SEO is actually alot of fun, and stress free from an SEO perspective. You actually need very few links with this method to rank well.