This study aims to analyze the transaction types and methods of new types of advertising such as social media advertising, retail media advertising, and commerce media advertising, and to explore issues related to the aggregation of advertising expenditures. To this end, in-depth interviews were conducted with key stakeholders in the new type of advertising market—including advertising agencies, platform companies, marketing experts, and influencers—as well as academic experts. Qualitative data were collected and analyzed using semi-structured questionnaires. The analysis revealed that the transaction methods of new types of advertising can be categorized into direct and indirect transactions, each with its own advantages and disadvantages. It was also found that while programmatic advertising is increasingly adopted in the domestic digital advertising market, an independent advertising trading ecosystem has yet to be activated, unlike in global markets. In addition, the study identified a problem in the reliability of advertising expenditure aggregation due to the non-disclosure of advertising revenue by global social media and domestic retail media companies. It was discussed that legislative approaches and improvements to the aggregation system are necessary to address this issue. This study is expected to contribute to understanding the transaction structure of the new advertising market and to provide policy implications for enhancing transparency in advertising expenditure aggregation.