Don’t waste money on bad URLs! Use this free AdWords script from contributor Daniel Gilbert to check your landing pages.
One of the classic tasks to automate with scripts is checking all your URLs for 404 errors. Google has their own Link Checker script, for instance. But this only tells you if a page is broken in a technical sense.
You could easily have pages that aren’t 404s but that you still don’t want to use in your ads. For example: