I think the strongest CTA in a comments sections is personality.
I often click on users who offer insight, respectfully argue a point, or are funny as hell. If I see a link (like you, or like chuck), I immediately categorize it as spam and move on. It's just too much for me to read, "I also wrote about this over here...", etc.
In fact, I'd much rather see someone write, "Hey, are you mind-melding w me? I DM'd you the link to what I wrote about this same thing last week. I think your idea is even better, esp. about..." That's someone I'm going to check out, maybe partner with, or buy something from.
Simply put, you are your own best linkbait. At least for me.
The only thing I would add is that in addition to linking to great, highly relevant content is maybe also having already acquired some trust, not only with the author of that blog, but his/her community.
In most instances I'm like Chuck (his tweet), and immediately think "spam," however, if it is someone I trust (and see everywhere), and know they provide good content I'll click on that link for a blog post, video, etc. that potentially adds value to my life. And like you said, if they want to sell from their own platform. Fine by me.
Yes, I think it can be done... but as you implied, you'd need to tread carefully on someone else's blog.
An additional problem would be how each blog handles links. Some eliminate them, or make them not clickable - killing their usefulness.
Your method is the best one I can think of... links only to highly relevant content.
Having said that, how would you feel about people very gently mentioning their Twitter profile? :)
Paul Hancox
@paulhancox

Do Calls To Action Work in Comments?
by Stuart Foster on June 16, 2009
Social media practitioners are probably really confused when reading this now. CTA in a comment? How the heck does that work? Won't it just get you deleted and ignored? Not necessarily.
Let's lay out what you need to accomplish with a call to action: clicks and conversions. If you can do those two things you are way ahead of the game. However, your conversion from a blog comment isn't going to lead directly to a sale. It can lead directly to content, advertising, or interactive features...not an ajax order form.
So what can your landing page for your cta be?
1. A relevant blog post. Think informative/useful and don't use any copy writing here. It should answer a question, provide deeper analysis or be otherwise relevant. It should funnel the lead in tighter if anything.
2. A relevant video. This can be just as valuable as a relevant blog post. However, it needs to be directly related to the post in question. You can't fake relevance no matter how hard you try.
Get the picture? It has to contain relevant information in order to be successful. Can you litter the page with links back to sales specific stuff? Absolutely, in fact I would encourage you to do so. However, your primary method of driving traffic to the sale should be the second step post cta (maybe even third?).
This works the best with a viral video. However, a relevant blog post (not canned copy btw) can be just as effective if it allows for a person to directly interact with and engage with your product/pitch in a place of your choosing.
You can't sell at another person's blog. However, if you are on your own territory you can sell to your heart's content.
Do you have any other suggestions on how this could work more effectively? Or do you think it doesn't work at all? Share your comments below.
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tagged as blog commenting, call to action in a comment, calls to action in comments, comment marketing, cta, cta in a comment, marketing through blogs, marketing through comments