Off page seo is all about building diverse quality of backlinks for your website. Make sure to go for natural and white hat techniques at first. Build not more than 8-10 backlinks per day. Blog comments can be spammy.
Yes I agree, link building strategies differ from niche to niche. Test, is the only way to find out if it works for you or not.There is no such thing as spam, if used right.
Test .. thats the only way to find out.
Even if you research competitors ... there is only so much you can see.