This is my opinion, not bashing you in anyway.
Your point is valid ONLY because this is important to you. (Email etiquette, written response).
Your judging him based these two things, which one may not be important to him at all, and two, he may be incapable of having. (Don't know his education, background, age, etc., lots of factors).
Lastly, you’re selling an item on Craigslist. Unless you have never sold something on Craiglist, EVERYONE knows to expect the dumbest, cheapest, ugliest, degenerate you have ever had the encounter of meeting with. If you’re looking for someone intelligent, sell them on eBay, but not always either.