To play devils advocate, this is a community forum that allows advertising not an advertising site. If you want to advertise somewhere with one way communication try TV, radio or newspaper. If you advertise here, on a public forum, why shouldn’t the forum members be allowed to post their experiences with your shop or cheaper alternatives to the product you are selling? If you have truely great service or an honest deal on what you’re selling it shouldn’t be a problem. Sure, someone may suggest some no name ebay special as an alternative to the name brand you’re selling, but that’s an option the consumer has. If your product really is superior you wouldn’t be afraid to post why and educate your consumer as well as the other potential consumers reading the thread. If on the other hand your name brand product is no different from the 50% cheaper no name I think the forum as served its members by allowing them to see the cheaper alternative.
I realize you as a paying advertiser should be protected from completely off topic posts or flat out harassment, but to limit it to advertiser only posting forums seem to defeat the intent of a discussion forum.