I don't see why bumping a price on Craigslist is necessarily such a bad thing...
There have to be many cases where the person listing has no earthly idea how collectible his particular item is. What we might consider a huge score is actually someone who listed an item for way less than the actual value. Now, how honest is THAT? Really?
Has nothing to do with honesty, but a lot to do with integrity of the seller.
It's the sellers business to research an item before he offers it for sale. Once he prices it, he needs to honor his price, even if he's underpriced. It's not the buyers place to inform a lazy seller about the true value of an item.
Like it or not, if you are offering something for sale, you're in business. And if you don't do your homework, that's your own fault, not the buyers.