How do I know what links are bad enough for the Google disavow tool?

[BallyhooLtd]

I am currently working for a client who's back link profile is questionable.  The issue I am having is, does Google feel the same way about them as I do?

We have no current warnings but have had one in the past for "unnatural inbound links". We removed the links that we felt were being referred to and have not received any further warnings, nor have we noticed any significant drop in traffic or rankings at any point.

My concern is that if I work towards getting the more ominous looking links removed (directories, reciprocal links from irrelevant sites etc.), either manually or with the disavow tool, how can I be sure that I am not removing links that are in fact helping our campaign?

Are we likely to suffer from the next Penguin update if we chose to proceed without moving the aforementioned links? or is Google only likely to target the serious black hat links (link farms etc.)?

Any thoughts or experiences would be greatly appreciated.

[Valarlf]

This post can help http://www.seomoz.org/blog/googles-disavow-tool-take-a-deep-breath

There are many free and paid tools that can help determine if you need to delete a link
http://cyrusshepard.com/boom-1-email-60-bad-links-gone-4-tools-for-easy-link-cleanup/

If you understand Spanish this post can help
http://luissobrevilla.com/como-eliminar-backlinks-de-mala-calidad/

[Debdulal]

This is another tricky situation. I think the message you have received is not about Penalty, it is just a precautionary message send to you just to inform that the link profile does not look natural and needs some pruning. What I believe is that if the links not coming from low quality link pages, directories, forums, web 2.0 sites etc [I am assuming that they are at one point built by an SEO company], you need to get rid of them.

_Take it as precautionary measure because your link profile has already raised the flag of spam and therefore, it is your duty to clean it. It is better safe than sorry. And Losing one or two keyword rank is far better than losing all the visibility altogether. _