Well....I've been through this before and it always freaks folks out...but here goes.
All the methods they tell you about color of beak, legs, comb, wattle are faulty....I've butchered good layers based on this fallacy.
Also, the width of the pelvic chamber is another fallacy....some gals just have different bone structure and I've also butchered good layers trying to use this method as well.
The only way I've found that one can truly tell if a hen is really laying? Wait until night, take a hen off the roost. Glove up, insert a finger gently in the vent and palpate the intestinal wall. If you feel an egg, that hen will lay the next day. If not, she won't.
I mark the ones that don't have an egg. The next night I do all the chickens the same way once again. The hens that are unmarked that have an egg are my daily layers. The hens that are marked and still do not have an egg are tied and will be killed the next day. The marked that have an egg, I just assume they are an every other day layer that didn't lay the day after the first check.
It's been a pretty good system for me and is pretty foolproof. I've not killed a good layer since using this method.
Contrary to what some may think, this does not harm the bird if it is done gently and efficiently. Been doing it for about three years now without any ill effects in my flock.
Of course, they look at me a little strangely the next day but, do you blame 'em?