Don't rely too much on tools. Good links sometimes gets flagged on automated tools. Manufacturer will have eCommerce sites linking to them. It'll look like networks - eCommerce sites sometime have multiple stores. Perfectly natural. News sites frequently have their content syndicated so they tend to have lots of low quality links. Also natural.
You can usually recognize bad links yourself.
Was the link editorially given?
If there are a lot of optimized anchor links, it probably wasn't. Are they guest posts? Web 2.0? Forums? Foreign countries? Is there unique content on your client site (ie - is there a reason that all these sites are linking to your client?)
I mostly use ahrefs.com
. It's rare that any further investigation is needed. Usually you can see pretty clearly if the links were because of an event, a new invention, great content or if it's artificial.
In other words you can see if a link building campaign was done and you can tell if it was based on content or "link schemes".