I hope this helps,
You can do it but the link juice you get out of this is negligible. It is far more better to post on different sites hosted differently. The effort you'll be inputting this way doesn't justify the outcome. For it counting as spamming, if you still want to do it, do it so that you post intelligent unique comments every time and only to the blogs that are relevant to your site or it might raise a red flag as blog posting is the most commonly known way of spamming, but as said before the return you get really doesn't justify it.
Hal Smith
URLdreamer Consultant
If you are comment on the article by the same author, First of all it won't worth because you will not get a backlink. And as you asked that who many comments can we do in a day. You can comment as much as you want to the different blogs.
Definitely different sites if all you want is back links. Just try to find sites that are relevant to your niche and actually give quality comments. Search engines are getting smarter. Quality is always better then quantity. Your best bet is to stick with relevant sites and engage in the conversation that is already started in the article and comments. Sharing useful insight on the post makes you more relevant to the searches and the other commenter's which may lead to them visiting your site in the future.
There is diminishing returns from multiple links on the same site, 1 link from 10 different sites is way better than 10 links from one site (or common IP address)
Comments are one of the most common backlink sources generated by automated spamming software, so at least distinguish yourself with insightful comments only only on articles relevant to your site.
One tool to help find relevant sources.
http://dropmylink.com/
Can we do blog comment on the same blog but different article by the author? It won't count in spamming, won't it? How many comments should we do in a day? Please tell me these three things?
Thanks in advance
