I'd offer different advice...
List the phone 100% honestly. If your phone has light scratches for example, take pictures of them so people know exactly what to expect.
I've also sold phones that were rooted and rommed. I then offer to answer any questions the buyer would have and get them started with making any changes they would want. Many people want a rooted phone but simply don't want to, or can't do it themselves. Offering technical support may take an hour or two of your time eventually but it may make someone pay a little extra for YOUR phone. Also, I always offer to return the phone to stock, unrooted if the buyer would prefer.
Lot's of options...but lying about the phone being brand new is exactly what's wrong with eBay and I wouldn't recommend it.