• Am I getting the best spot at the best price?
• Has the spot already been tested?
• Does the spot have stats and data to back up its price?
• Are you prepared for traffic fluctuations?
• Do you know if the spot allows all content?
• Does the site limit you in how you can display your ad?
• Does your spot allow all types of creatives?
• Are you watching your ad rotation?
• Is the price right?
• And most importantly, do you trust the seller?

Read more here:

From Newbie to Media Buying Authority – Part 2 – 10 Things to Ask Before Buying Flat