Is the owner of a buying and selling application, which allows users to post advertisements and pictures, sinful when some users post pictures of women in sections designated for women, which men then see, or when women post their personal pictures as profile pictures?

It is not permissible to advertise or promote anything that includes images of women, due to the sin that results from it. It is also not permissible to look at images of non-mahram women, whether directly or through pictures, due to the temptation involved. In fact, pictures can be a greater source of temptation because they are often enhanced and beautified. The one who publishes them bears the sin of publishing and looking at them, as well as the sin of everyone who looks at them. This matter is not simple; rather, it is grave, and those in charge of websites and forums bear sins commensurate with the number of viewers.