Bannou Kanteishi Q No Jikenbo summary:

From MangaHelpers: Yuto works for a magazine company known as "Kadokawa". His current project revolves around a mysterious phenomenon occurring inside the city. Someone or something has been placing stickers of a sumo wrestler's face all around the city in various places. No one knows who is placing the stickers or what their objective may be, but these stickers have been showing up in places for a while now. Yuto now needs the help of an appraiser to solve this mystery. Searching through the web, he finds an appraiser known as the "Appraiser Q". Her name is Rinda Riko, and she has the ability to appraise anything (or anyone) and solve any mystery thrown her way. [DrCoke]