Your talking about a Google adwords campaign.
It's down really to what you want to achieve and your budget.
Personally I think it's best to get a feel for it yourself, and get to understand, even at a high level how it works, fully appreciate which keywords work for you, a rough idea of conversion costs etc before handing over to a managed campaign. But thats me.
If you've no interest in doing it yourself and want to purely outsource it, then be clear on your budget, and what your aims and targets are.
If you're spending less than
