The detail and precision of the more massive and complex crop circles appear to be quite beyond the skills of hoaxers. And, the time taken to create them appears to be too short for hoaxers to be able to manage.
Also, there's the many different scientifically verified distinctions between the plants and the soil in bona fide crop circles vs hoaxed ones. See Linda Moulton Howe's book on that score. Her website might have some bits available publically.
"Bona fide crop circles"??
nee-nee-noo-nee, nee-nee-noo-nee, nee-nee-noo-nee
Yeah, right.