Getting linking juice from blog comments

I have all was have wondered if it was smart to allow people to post backlink comments into your wordpress page. I believe this would done within reason, for example if someone is backlinking to me from a fitness site but i am a site on dogs then its not wise, but if we are talking about the samething then why not?

Also, is there a was to check if the site who is backlinking to me is using a plugin that is stopping me from getting link juice from him while he is getting from me?


Thanks
Michael