Interesting debate going on here, my take on it is.
1. Most aspects of what has been said is irrelevant. Bankerdanny's motivation to inform the seller was based on his "not having squat" to buy anything on craigslist. He saw something he wanted, was unable to buy it, and that did not sit well with him. I fail to see the "good Samaritan" angle here as if he would have had the money, he would have bought it.
2. The ad in the first place was probably fake. How many bikes have you seen on a craigslist ad that weren't poorly lit, low resolution, less than desirable angle, etc. etc. --good, clear pictures are few and far between and usually taken with someone's jitterbug or aging cricket flip phone. Someone also astutely pointed out the nice manicured lawn and background. This picture was pilfered from somewhere on the internet.
3. No one with a 69 would ever do this. Everyone with a 69 thinks they have a sandcast. Everyone with a 70 thinks they have a sandcast. If it's not a sandcast then it has "sandcast parts." People don't even know what a sandcast is, but they are prone to think that they could have one and that it's worth a lot of money.
4. And here is the bottom line. Someone posted a fake ad about a bike on the internet to farm email addresses. Bankerdanny donated one to the cause. There was never any bike and BikerDanny made himself look selfish and spiteful and will be rewarded with more penis enlargement spam in his inbox. The end.