The benefits of real-time bidding (RTB) seem obvious, but as a percentage of the display advertising market, RTB’s growth has lagged many observers’ expectations.

So what gives?

According to a study (PDF) conducted by Advertiser Perceptions and released this week by Casale Media, approximately half of media buyers and sellers are already participating in the RTB ecosystem, and significant growth is expected over the next year, but both sides still have a number of concerns that are holding RTBs back.

The biggest issue for media buyers is quality, with more than three-quarters indicating they’re concerned about the impressions they’re receiving. Given that half of online ads aren’t 50% in-view for even a second, it’s not surprising that these media buyers said they’d probably spend more through RTBs if a viewable impressions standard, or something similar to it, were applied. Following quality, 70% of media buyers polled expressed concern over brand safety and 65% were uneasy about the transparency of the RTB process.

For media sellers, commoditization is by far the biggest concern, with 84% of publishers surveyed indicating that they fear RTB could devalue their inventory. Also of importance: the elimination of the “human element” in the ad sales process. A not-insignificant number (25%) of those most concerned about what RTB means to their relationships with media buyers, “feel that face-to-face negotiations and dedicated account management are extremely important if they are to use RTB in the future.”

Interestingly, despite the growing use of RTBs and expectations that they will become more and more prominent, both media buyers and sellers made it clear that further education is needed as there is confusion about the components of the RTB ecosystem. According to Casale Media, “Respondents want a clearer explanation on differentiators between RTB, private ad exchanges, supply-side platforms (SSPs), demand-side platforms (DSPs), agency trading desks (ATDs), and data-management platforms (DMPs), and how these are different from ad networks.”