What is the official policy for Vendors hawking their products as a solution to someones question?

Is it encouraged? Discouraged?

We have a vendor here: [thomas-hansen](https://stackoverflow.com/users/29746/thomas-hansen).

Hawking his stuff:

* [aspnet-control-in-jquery-modal](https://stackoverflow.com/questions/313611/aspnet-control-in-jquery-modal#313623)
* [aspnet-based-workflow-engine](https://stackoverflow.com/questions/315758/aspnet-based-workflow-engine#315977)
* [how-can-i-find-out-how-my-site-was-hacked-how-do-i-find-site-vulnerabilities](https://stackoverflow.com/questions/308406/how-can-i-find-out-how-my-site-was-hacked-how-do-i-find-site-vulnerabilities#308643)
* [asp-ajax-calendar-extender-and-displaying-time](https://stackoverflow.com/questions/279552/asp-ajax-calendar-extender-and-displaying-time#316059)
* [for-our-next-project-i-would-like-to-get-into-some-ajax-to-improve-the-user-int](https://stackoverflow.com/questions/286311/for-our-next-project-i-would-like-to-get-into-some-ajax-to-improve-the-user-int#304632)

How should I vote on these?