Doug King says:

Just because it's not specifically prohibited, that doesn't mean it's A-OK.

Placing advertisements in a discussion groups is always considered rude. It's
the uenet equivalent of telemarketing.

Quite so. There is a newsgroup specifically for this task -
rec.boats.marketplace

As previously mentioned, no-one minds the occasional "Hey, guys, I have a tool
to sell - anyone interested?", but a whole post of tools to sell would come
under the heading of spam in most groups.
If it's done once without comment, and doesn't recur, then fine. If it's done
repeatedly, then it's a No-No. If it's done once and someone comments - well,
that's what we have here ;-)

Steve