Domain blogs would seem like a good place to sell domain names. There is a captive audience of people within the domain business, and many people who read blogs buy domain names on a regular basis. Unfortunately, the comment section is not a good place to sell domain names.
I have to deal with comment spam on a regular basis. Usually, the spam is caught by the Akismet spam filter, but occasionally it gets through. Akismet is not as good at catching people trying to sell domain names as it is at catching spammy links to porn, pharmacies, and other blog comment spam. This means that I (and other blog publishers) have to manually mark these comments as spam.
The vast majority of comments that have domain names for sale contain domain names I wouldn’t even take for free let alone buy on the aftermarket. These, in particular, are super annoying. However, any spammy comment selling domain names is annoying because it takes away from the discussion. Imagine being at a domain conference and having a small group discussion and someone joins the group and says, “hey guys, I am selling Crappy-domains.garbage for $1,000.” People would be rightfully annoyed and probably slightly amused.
There are many venues for selling domain names. There are marketplaces and auction houses, sections in domain forums, and private brokers and newsletters. I can understand why people would try to list domain names for sale in the comment section of domain blogs, but it is not appropriate.