Seeing this page is pretty highly ranked by the average search engine (google), outbound links from whs.org will probably carry a greater SEO weight than from random sites on the internet. I think this explains a bit the incentive to create links here to external blogs, reviews, commercial sites and the likes. Also, with the significant amount of visitors this site gets, it's also a nice way to create some traffic on your external site.
To me it's fine if people refer to their own content. That's why we have the option to link to your own blog. But:
* The content shown on this page should be usable and to the benefit of others. I don't want a review that essentially says: This is a great place. Been there on .. Nice to see... More in my blog. That's too little. If that's what you want, create your own page and do SEO on your own.
* Commercial links should be fully banned.
* In the long run it will actually ruin this page if we host low quality links.
With regards to hotel recommendations etc. it never occurred to me that people would post sponsored stays etc. But yes, these should be banned, too. When I give a recommendation it's normally because it's something special I noticed and enjoyed.
Going forward, some of it should be resolved when we finally deal with the new version. It has a publishing workflow and Els can schedule posts as well as comment on them prior to publishing. So she could return a post that is lacking in quality or depth to the author. It would probably also help to provide a bit more instructions of what a post should and should not contain. E.g., don't copy content, don't use this page purely for marketing, ...