This policy covers not only posts by vendors, but also posts by others concerning vendors....
1) Any experience/comments about a vendor must be based on personal experience purchasing from that vendor. Not what happened to your friend, not whether or not you like them personally. Personal business experience. Off-handed, side remarks are included in this.
2) Vendor Product Announcements (or such posts on their behalf), sale announcements, etc, go in the appropriate forum -- most belong in the Vendors and New Products section. Those which are Research-specific may be posted in the Research Forum. Understand that posting in the latter restricts your audience.
3) Vendor Announcements that are plagiarized from another message, or announcement (regardless of whether or not it originated on the forum) are not allowed.
4) Replies to Vendor threads are not to include competing offers from other vendors, places to buy it cheaper, derogatory comments about the vendor or product, etc. This does not mean that two vendors cannot have two separate threads offering the same products, just that they cannot post about it in each other's thread, nor can they refer to the other thread.
This also doesn't mean a vendor cannot post in another vendor's threads -- a lot of the vendors are friends, as well as customers of one another!
Remember, our vendors are the lifeblood of our hobby. Without them, we're done. A diverse group of vendors that support us, our hobby, and our launches, are a benefit to each and every one of us.