It is the quick and the dead in the marketplace when a good deal appears. If you are not on the ball and watching, don't expect to be spoon fed information after the sale is over.
I am happy to see anyone make their first post a "for sale" notice if they are offering an interesting uke for sale at a reasonable price. Who cares how many posts they have if the uke is good? If you want to check out any seller, whether they have 1000 UU posts or just one, then do your own homework, do not rely in the number of posts on UU to work out if the sale is good or bad. And I don't really care if it is their one and only post either.
The marketplace is for buying and selling real ukes with real money, it is not a collector's corner for collectors to gather info or to discuss nice ukes. If you want to talk about collecting or gather data for your files to sell or trade, I think you should use the Uke Talk Page.