What to do about it, which is usually nothing.
WHAT PEOPLE SUSPECT
Bought links Spun or duplicated content Hidden text Fake reviews Doorway pages
WHAT YOU CAN DO
Report spam through the appropriate channel, which exists for this purpose. Do not expect a fast or visible response.
WHAT YOU SHOULD DO INSTEAD
Concentrate on your own site. Time spent analysing a competitor's tactics is time not spent improving your content.
Tactics that currently work frequently stop working, and sites relying on them lose everything in an update. Sites built on genuine quality do not.
WHAT NOT TO DO
Copy the tactics. If they are penalised later, you are too. Attempt to harm them, which is both unethical and largely ineffective.
THE HONEST ASSESSMENT
Frequently a competitor ranking better is not doing anything suspicious. They have more content, better content, more links, or more local relevance.
That is uncomfortable and more useful to know than the alternative.
THE PRACTICAL RESPONSE
Look at what they actually have that you do not, and close that gap.
