Meanwhile I posted my car for $5 and got multiple offers within 2 hours. In fact, the ad was so successful with selling my car that I actually couldn't keep up with it and basically ended up selling to the first person I clicked reply to.

Maybe your product was bad? Do you live in an area devoid of people? I'm sure I also got about 10% of people trying to scam me somehow, like convincing me to come out and then claiming they didn't bring the money, but eh, I didn't feel like going through the trouble of putting it on eBay