Effectively managing a PPC campaign is something that takes both knowledge and planning. If you are not familiar with the adserver(s) that you're using, and if you don't make sure that all the groundwork is done (like having individual landing pages for each ad), then your campaign will be costly, short-lived, and see a terrible ROI and conversion rate.

If you don't have the expertise yourself, then, you have two choices: either hire a PPC manager, or outsource you campaign to an agency. If you decide to go with an agency, what you don't know about them (and the industry) might not kill you, but it can still kill your profits by exhausting your budget and not generating any new revenue. According to Search Engine Land, there are 5 Secrets that PPC Agencies Don't Want You to Know. These are:

Most agencies specialize in consumer search marketing and their services are inappropriate for your unique needs as a B2B company.

The agency business model skews in favor of the largest spenders and under-serves the majority of B2B advertisers.

Agencies will never understand your customers and your business as well as you, especially B2B firms that sell more complicated products and services.

The need to coordinate with outsiders implies latency and information loss, meaning you lose the flexibility and agility to react quickly.

Outsourcing means losing control over a critical portion of your demand generation strategy to outsiders who may have different incentives than you.