Here is a direct quote from the Tweeters guidelines that makes it
pretty clear (emphasis added). For example, Paul Bannick's course is
sponsored by non-profit Audubon, so would qualify for a one-time
announcement on Tweeters.

Marc Hoffman
Kirkland, WA
tweeters at dartfrogmedia dot com
www.SongbirdPhoto.com

>Other categories of objectionable postings include:
> * ...commercial advertising (as distinguished from product
> endorsement). It is fine to post "I prefer such-and-such model of
> binocular," or "I want to tell you about a great new book," but it
> is not appropriate to say "...and you can buy it at Bob's Camera
> [or Greenleaf Books]." However, one-time announcements from
> not-for-profits about a new publication, or service, or event, are
> appropriate for posting to Tweeters.


>On Feb 12, 2013, at 12:49 PM, "Tracey Kidston photography"
><info at traceykidstonphotography.com> wrote:
>
> > Hi Everyone,
> > I wanted to know what are the "rules" in regards to advertising
> or promoting trips both local and international?