I could never find the jackets I prefer, in a physical store. So I buy a size too big to be safe.
I've done the dodgy a handful of times - tried something on in store to get a feel for the size...... then still guess ordered it over the internet . I say guess order as it's still a lottery if it will fit exact or not. I've not got it wrong thus far (not that I've done that method regularly, last time was May last year).