Fragmented Audience: The numerous TV channels available and large number of radio stations available to consumers in any given market are miniscule compared to the number of sites available to online audiences
Selling practices vary widely, including scheduling patterns, post-buy analysis
Budgeting: Must determine whether online placement is an advertisement or a promotional budget item.
Cost: CPMs are relatively high for ads that are intrusive or highly-targeted.
Special creative may be required to maximize impact
Size of ads and length of messages is still limited by size of screen, bandwidth
Accidental click-thru by the consumer will increase the cost of the ad to the marketer but don't expose the consumer to the message
Exposure: Consumer connection with content and placement varies widely from site to site
Measurement and Accountability: Research across the industry is still nascent and many sites and services employ unconventional and/or unreliable metrics to define audience and impact. Additionally, while it's a given that online ads have the ability to motivate consumers, proving efficiency remains elusive. Concern has grown across the industry in recent years regarding fraudulent measurement and reporting of consumer exposures to advertising
Advertising Aversion: Online ads such as pop-ups, banners are viewed by many consumers as too intrusive. Blockers and other forms of avoidance are a problem for advertisers
Fraud: With measurement minimal or lacking altogether, the digital industry must confront controversy regarding criminal activity surrounding ads, and whether actual consumers or "bots" have actually accessed ads online
Do Not Track Law: It is illegal for advertisers, retailers, etc., to track consumers' movements across the Internet
Privacy issues: In addition to the legality of the practice, consumers are not receptive to online advertisers, retailers, etc., tracking them. Many find ads following them across sites to be "creepy" or offensive, even "evil."
As the adoption of traditional broadband service has slowed in recent years, a growing share of Americans now use smartphones as their primary means of online access at home. Today one-in-five American adults are "smartphone-only" internet users – meaning they own a smartphone, but do not have traditional home broadband service.