What criteria should I use to evaluate an SEM vendor?

Amongst many of the criteria, the most important should be :

• Talk to existing customers and ask for feedback
• Ask for a free audit of your Google Ad campaigns
• Does the vendor follow a goal-based marketing and advertising approach
• Does the vendor have a team of creative designers and web developers who can create campaigns as and when required.
• How does the vendor plan to reduce costs without compromising on leads
• How does the vendor do lead tracking on behalf of the customer.