Hi GregM:
We have a policy that a one-time link can be provided to yoga and spiritually related products, teachings and services. Admittedly yoga mats (and clothing) are not much in that realm, and we no longer approve first time ads for those. So you are not likely to see any new ones along those lines.
Regarding limiting the posting of links until after so many posts, that would be too restrictive, because people often come to the forums with important and relevant information to share via a link. We require a description (at least a sentence or two) to be provided with any links posted, so readers can make a judgment on whether to click on it or not.
For more on the posting guidelines,
see here.
We do have a restriction on new members using the forum private email service until they have participated in meaningful discussion here for a while. This prevents spammers from coming and using the email service. As far as we know, this works quite well.
Thanks!
The guru is in you.