I know at least personally... when I post "IN" I'm 100% sure that I can make it without a doubt. I'm sure most people would definitely agree as well. Obviously if a person posts that they are coming, they should make every effort to, as other players and the hosts themselves are relying on them to come for various hosting reasons (game balancing and fees for example), thus they have a bit of a responsibility to show up if they posted "IN".
Of course, LIFE happens and sometimes people really need to back out for whatever reason it may be, if they honestly can't make it.. well, then they cant. Simple as that. I know I was 100% ready to go for OP: Rhino last summer, but work ended up fucking me over cause they needed me for inventory, and there was no way I could get out of it.
Guardians of Asgaard - KF25 -
Primaries: LCT AS VAL, LCT AKS74UN, VFC M4 CQB Mk2
Secondary: Latino heat, TM Glock 17