NGC and PCGS are a joke. All grading companies are a joke.
usually people who balk at the ancients are at least fine with the moderns. i'm generally fine with both, though i prefer ancients.
i certainly wouldn't buy from a tourist trap place, or ebay, because both of those places are likely to get you an obvious fake.
but i feel pretty safe buying from known dealers who've been in the business for 30-40 years, and cross checking their coins against known dies in catalogs that are between 20 and 200 years old.
most ancients really aren't that rare - some roman emperors minted almost 100 millions of silver coins a year around 200-300 AD. and the athenians pumped out a huge amount of owl silver tetradrachms between 450 and 400 BC, over 10 million total. it was so widespread across europe and the middle east that it sort of became the default currency, and some other civilizations made their currency look similar with an owl on it for the next 100-200 years.