If someone is between sizes, do you go smaller and adjust the seatpost, stem, and bars to fit?
IMAO you can adjust to go bigger. However, in order to get a bike that is a little too big smaller you need a hack saw…
It depends on the frame and where exactly it doesn’t fit, but -
for me, where the perfect bike would be a 57 in the vertical plane, and a 55 in the horizontal, I went with a 55 with 2cm of stack under the stem and a longer seat post.
I concur, go smaller.
You can always buy a longer stem add spacer and raise the seat. Otherwise you could be SOL.