I bought a (time sensitive) product that was advertised as one day prime delivery. When I checked up on it, it showed me that it is set to arrive much later mid-week (+3 days than advertised.)
On closer inspection, I realized that I had used the 'Buy Now' option that only uses the Prime Day shipping option.
To me, that is a solid dark pattern and is making me seriously consider cancelling Prime for the first time in 15+ years.