Local SEO & Lawyer Marketing expert. I help businesses who want to rank for competitive keywords in saturated markets beat their competition through sustained white hat SEO practices.
I am a contributor to the annual Moz Local Search ranking factors study and author of How To Perform The Ultimate Local SEO audit.
It's true that link building has become more difficult and the game has continually evolved. Back in the earlier years of my SEO career we used to engage in comment posting on blogs and forums as a way to get backlinks easily. We no longer engage in these activities unless they're under very specific circumstances.
First and foremost you never really want to have the attitude of "let me try to manipulate the search engines". You may not get caught tomorrow or in a month but eventually it will catch up to you and when it does the amount of work trying to lift a manual or algorithmic penalty is simply not worth the risk. I am mainly talking about people who use this as their primary means of link acquisition.
On the other hand there are cases where it's OK to do it. But it should be approached with a different mindset. Your thoughts should be somewhere along the lines of: How can I post a thoughtful and substantial comment that will provide clear value to the readers? If you do this and other site visitors find your answer actually useful, then having the link could provide some value as an interested user or potential client might follow it to your website. If you are doing this with a purpose that's other than just link building there could be some benefit. I wouldn't do it in any other case.
Any company that is just trying to get links to their website is not looking at the long term big picture. The best way to earn links is by doing real company stuff. You want to earn natural links and diversify. Sticking to one method is not a good idea.
Now for some practical advice. For example if you donate to charities they might provide a link back to your website. If you offer a scholarship for students, .edu domains will be willing to link to you. Sign up for HARO and respond to as many interview or PR requests as you can. If you host events there are tons of opportunities to list the event and link back to your website.
The most important thing to remember is that your anchor text should be natural and its quality over quantity with links.