But the exchange is full of people looking to make a buck. That's cool, free market and all of that, but your sales threads should reflect how you approach the hobby.
When I started collecting knives and buying customs many years ago it was a very honorable community. I buy and sell knives but for me it is purely a hobby. But now there are a lot of people here that view knives as nothing but a business and it has become very cutthroat. For all I know the flippers living in their mother's basement sit there all day and do the same thing with baseball cards, expensive tennis shoes and sports memorabilia.
My explanation is this- if you sell a knife today for $100, then tomorrow you won't be able to sell a similar knife for $150, so it limits your potential profits. But if there are no prices listed you might be able to convince someone tomorrow that your rare superknife is worth $175 and you make more profit. So if your goal is to make more profit then you remove the prices. But considering that the few people left that view knives as a hobby like to know what various knife models sell for, if you are interested in serving the knife community of hobbiests you leave your prices in your ads. So which side are you on? Me, I always leave the prices in my ads.
If the rules of the forum said you had to leave prices, people would be forced to do it. The logic is probably that sellers are free to do whatever they want but this site has a long list of rules covering everything else. If it came down to it though I think I would rather have a forum rule that required a seller to post a photo in their ad, a reasonably good photo. I've been on forums that catered to hobbiests that required photos with ads, and if you didn't post a photo they would quickly delete your post.