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

SEOMozBlog - Link Forensics: Finding Shady Links Before Taking on New Clients

Good article on checking the previous SEO for prospective clients, some good advice on links checks and discovery of cloaking techniques:
Link Forensics: Finding Shady Links Before Taking on New Clients