Search Engine Guide - A Case Study of SEM Campaign Failure and Client Refunds

Interesting case study of unhappy clients in two separate PPC campaigns and how they were resolved:
A Case Study of SEM Campaign Failure and Client Refunds

Search Engine Guide - Five Common Paid Search Mistakes That Can Sink Your Campaign

Good overview of the mistakes new PPC users can make when starting up a PPC campaign. Another great article by Jennifer Laycock:
Search Engine Guide - Five Common Paid Search Mistakes That Can Sink Your Campaign

Kalena Jordan: How to Turn Around an Unprofitable PPC Campaign

Kalena Jordan's excellent article about dissecting problems in PPC campaigns.
How to Turn Around an Unprofitable PPC Campaign

Redflymarketing.com PPC Articles

Three detailed PPC articles from Redflymarketing.com make good reading for those providing PPC services:

Do You Make These 12 AdWords Mistakes?

Dynamic Keyword Insertion - The Ultimate Guide

10 Ways To Increase Your Adwords Quality Score - A Mini Case Study