I'm probably not the best person to answer this question, but I'm going to try. I'm still trying to remember identifying characteristics
A look at the underside and foot of the nem is the best place to start. The foot and underside of the oral disk is usually a creamy white color. The underside of the oral disk also has white bumps (verrucae) that has a characteristic pattern (that's where I get lost).
Sometimes a view of the tentacles and such can give you a little bit of info, but if the nem is in poor health the color and tentacle shape won't be characteristic of this kind of anemone, and sometimes different types of nems, even when healthy, can look similar.
Sometimes their choice of real estate in the tank can give you a clue, crispas are primarily sand dwelling anemones. There are exceptions though. Mine hangs out with it's foot secured to a rock with the bottom of the foot just barely touching the sand. It's been in the sand before, as well as a little higher off the sand.
I'm sure there's more to add, I just don't remember it right now

But there are others who are much better at this than I am who will hopefully chime in