As the above poster mentioned, skepticism is fine, but I think you need to be careful not to fall prey to turing speculation into evidence, and also considering all possible scenarios/outcomes instead of just those that point towards your conclusion.
What I mean by the second part is when you come up with a reason to question a claim, that doesn't automatically weaken or invalidate the claim. Your first contention is basically "how can it be racism from just a craigslist posting?", that is, how did the assailants know he was black? Well, it's possible the assailants became more aggressive at the time of the meeting, after seeing the seller was black. Or perhaps the seller included a name more common with people of color. This is not suggesting that either absolutely is the case, but they are both likely and not uncommon scenarios in the present day. If you're going to begin speculation in this manner, it is only fair and reasonable to consider how your conclusion might also be falsified, considering alternate and equally plausible scenarios.
Or in the case of the cuffs, for which your comment seems to rely more on a rather dismissive statement of ignorance - cuffs certainly can and do cut and tear into skin when not used properly. Just do a quick image search for "injuries from handcuffs" (warning, some images on this search are nsfw and unpleasant) and it's plain enough to see multiple examples of damage from handcuffs, whether it be bruises or lacerations - it's fairly hard metal tightened hard around a fragile point on the human body. It's not hard to imagine how that could do damage or how bad the damage could be when used improperly (Intentionally or not). Yes, it is important to get this verified (a picture from the author would do nicely), but the basis of your skepticism is not really set in reality, but seemingly in raw skepticism.
The point I'm trying to make is that it is good to withhold judgement, but the attitude and the questions you raise really aren't sound, and instead appear almost vindictive.
Be skeptical, but part of that requires being a bit dispassionate and openly considering reasonable possibilities. It does not mean building up speculation as the foundation for a conclusion. It is possible this is a hoax, as you say. But to suggest it "screams" hoax is inaccurate.