This study was done at my uni, and the legitimacy and rigor of it was questioned and investigated by the university. However, it was ultimately not deemed to be inappropriate. Some interesting info is that the single picture that was shown to the "jury" of a student was handpicked by the author from Facebook, and that the jury consisted of high school students.
They don’t say whether the author knew the grades when selecting the images. They also don’t say whether the jurors knew the grades. As long as they didn’t know I doubt that it had an impact on the study.
You could skew the results if you knew the grades but it wouldn’t be easy.
The reason it was questioned was that some women felt uncomfortable by having their images pulled from social media and rated for attractiveness as part of the study, without having been asked or informed. But ultimately the ethics people decided that it was fine after all.
More info: https://www.svt.se/nyheter/lokalt/skane/snygghetsstudien-ar-...