Poor in-person interview logistics/experience. I was in Boston for personal reasons but had to change my train to make it to the office in time. Wayfair refused to reimburse me, even after their recruiting rep said he 'likely' could.

Additionally, top-level managers were unprepared and somewhat unprofessional.

Business case: They presented me with an email outlining their problems with a recommendation and suggested ways I might improve it. They also conducted a 'lightning' round of mathematical, statistical, and programming questions. This round was a little all over the place (and not tailored to my resume) and was done in a binary yes/no fashion.