There are surprisingly few if you manage your campaigns carefully and stay on top of your spending and conversion rates. The biggest one is that as bigger businesses continue to wake up to the potential of search marketing, and funnel more of their advertising spend online, the cost per click of more competitive keywords can soon get prohibitively expensive for smaller advertisers, but by getting clever with your use of long-tail keywords there are still plenty of opportunities to reap real rewards from PPC advertising.
The key thing to remember is that you have to pay for every click whether or not you convert – so it is important to keep track of the metrics and make sure you’re getting value from your investment.
Ryan, D., 2016. Understanding digital marketing: marketing strategies for engaging the digital generation. Kogan Page Publishers.