This Is My Insider Selection Matrix to Hiring the Right Agency | Entrepreneur
Briefly

Be prepared to identify a few things internally, including your budget, end goals and capacity to work with an agency. Identify your internal KPIs as well. You might not know how a particular agency will report, but if you can share your own measurements, it's an important step toward success.
I commonly hear people say they don't want to share their budget. We always have it on our first call because you could waste your time with agencies outside of your budget; I think this is an important discussion.
Your end goals could include business goals and agency goals. It's important to share why you're hiring an agency because it really helps an agency plan whether they would be an effective partner; agencies don't want to fail either.
Also, create a list of questions you will ask. I personally think many people focus on the wrong questions and everyone as.
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