not a lawyer by any means, but this is a difficult case which for sure both sides of the coin have merit.
If asking prices are listed on brandbucket and you can see it and note down all of them,
the next day do the same thing and see which ones are not there or sold, then you can gather the sales info.
(unless some sales were negotiated for a cheaper price).
so basically Brandbucket is asking to the seller not to divulge the sales prices, but if the information is attainable through public means and it's not like you're using these names on your products or tshirts, so youre not infringing their trademark or acting illegally. If it was so , it would be the end of investigative journalism.
Giving information about a trademark is not infringing on the trademark itself, so even if the names are "unique" , it would be hard to prevent anything of this sort, even legally.
The only way would be to put make offer, and have internal negotiations, and keep it that way which would definitely turn off alot of buyers as they won't see the price from the start.
But for sure the buyer might be really ticked off and might not come back..
Namepros doesn't have a NDA, so often times, a quick search brings up threads of 2-3 years ago where you bought and sold for 50$ and it can work against you now..
I love namepros , but just saying