I was an admin there. Valuable tourism section.
I could see the moderation logs. Obvious selling all over the place, I knew who the sellers were.
I'm a black hat and I never sold a placement at DMOZ.
For real.
I did place one of my sites though (100% legit) into the category.
I liked DMOZ, I think it was a cool project.
Google today is doing a LOT of hand quality control. Google is essentially a larger DMOZ with tons of automated stuff but deep down they categorize things and sort them kinda like a directory would. Note that Google's initial crawl seed was DMOZ for many many years. Sites in DMOZ were highly trusted.
Google's end goal was to have a automatically built index which was as high quality as a human made one. I think DMOZ played a big part in it.