|>>|| No. 22892
I'm not sure it's still the case, but at one time there were previews and there were "previews". For some reason the film industry is adamant that releases happen on Friday, so you went through this phase of "Out Friday, preview screenings Tuesday, Wednesday and Thursday".
In terms of actual previews (for press, etc., as opposed to "previews"), one local cinema would happily tell anyone that asked what was coming and sell tickets for them on the day, but stopped the practice after a couple of hundred people turned out on the morning of one particular preview screening.