Ignoring the middle funnel:
It's common knowledge that many people engage with you because they receive education around their area of interest/expertise. These people sit in the middle funnel because they're unlikely to respond to a direct sales attempt but they're getting missed out of the marketing mix. Nurturing this funnel by providing relevant content including newsletters and e-books for example are all crucial actions that lead to long term relationships and customer loyalty, but they're often overlooked and the budget is spent elsewhere.
Not segmenting their audience:
Commonly, marketing campaigns are only relevant for one area or department only(such as accounts or HR) but they're directed to ALL departments. In this case, messages get diluted and have little to no impact because the information is vague and generalised rather than specifically talking to key people.
Not building trust.
Consumers are always looking for companies that they can trust. Many businesses offer an over-priced product and don't focus enough on their key messages which include reliability and quality. By focussing more on personal relationships rather than the product details (which are of course still important) results will start to improve.
Have you noticed a disconnect in this area in your business? What have you identified as the biggest waste of your valuable budget?