For a solid foundation, you may want to read these articles to start with understanding paid search 101:
The PPC (pay-per-click) advertising world is no longer as easy as choosing keywords and bid limits for a search engine or two. In order for your company to have sustainable success, you need to be strategic in your campaign management.
Learn how to advertise wisely.
Innovations & ROI
More and more companies are realizing the incredible return-on-investment that can be generated from properly managed paid search. Additionally, several innovations have entered the market since the early days of PPC: you should be taking advantage of them … before your competitors do. These newer channels include:
What to look for in a PPC vendor
Does the vendor have a team of dedicated marketing experts? Are the members aware of how to profit from the latest innovations in paid search? Most importantly, do the people who work on paid search know how to integrate with other marketing channels?
Finally, check that the agency is:
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