Its sure can be tricky to identify accipiters. But, it gets easier with time. Use this infographic to get an idea of what to look for in the field. One of the easiest field marks is actually their size. Cooper’s hawks are ALWAYS bigger than Sharpies. Females of both species are larger than males, but a female sharpie can be as big as, but not normally bigger than a male Cooper’s hawk.
Also, these guys are tricky! Its ok to not identify every single one. Sometimes its fine to just say you saw an accipiter and feel good about that.