I wouldn't go so far to say fecals aren't accurate, they aren't 100% but nothing is. Sometimes worms aren't seen, tapeworms are normally seen in person rather than on a fecal but they are short, white, "rice" like segments. Rounds are long, white worms that may be seen when heavily infested. Worms eggs are shed in the feces but not at all times, perhaps that's why you could say fecals aren't totally accurate but they are still the most accurate way to check for worms. With puppies, we will check fecals every time they come in for vaccines during the puppy visits so we make sure we find them. Signs could be diarrhea, lethargy, pot-belly, bloody stool, or even vomiting we've seen some puppies vomit worms up when they have so many! Poor things!