I really don't think there's anything wrong with changing your price and dishonoring an agreement if, due to ignorance of the product, you find out what you're selling is worth much more than you're asking.
How many if us have scored something cheap, and have known that you're taking advantage of the seller's ignorance, and laughed (and bragged) about it?
I know I have, many times.
It sucks when you're the expectant buyer, but bottom line, it's still the owner's right to change his price. It's his until money and product change hands.
I've been "burned" multiple times as a buyer, but I've also been lucky to find many things for a literal steal from uneducated sellers.
Remember, "there's no honor amongst thieves."