4. How to advertise on Usenet
The on-topic notice
Note the word "notice." A notice is a brief mention of the product with information about how interested persons can find out more. It's not a sales pitch. It's not an advertisement. It's not a "BUY BUY BUY" sort of message. It's a notice.
You are also strongly encouraged to keep such postings hype-free. What often works very well is to post information about your services or product and include a contact address, World Wide Web site, or phone number for people to use to get more information.
This is not to say that on-topic notices will always be welcome; the proliferation of inappropriate advertisements (ads posted in the wrong way to the wrong place) has resulted in all ads, even informational notices posted to appropriate newsgroups, tending to get a cold shoulder. You can help by limiting your ads to informational postings posted only where appropriate, and abiding by any local restrictions a given newsgroup's readers have placed on advertising.
*.forsale and *.marketplace newsgroups
For example, the misc.forsale.* hierarchy is full of newsgroups for buying and selling various computers, monitors, printers, devices, and so forth, as well as misc.forsale.non-computer.*, for selling stuff that's not computer-related. However, the misc.forsale.* policy is rather resistant to *commercial* ads - the hierarchy is intended as a place to post classified-style ads.
For example, Oxford has the ox.for-sale group, where classified-style ads are the order of the day.
It's generally considered rude, though, to crosspost a notice about your product to every forsale newsgroup, even ones on the opposite side of the country or world. Post your notice only to your local forsale newsgroup, if one exists.