It's a logic/puzzle game. In all truth, a mathematical formula could be derived that would offer the answer in a minimum number of guesses and amount of time.
I have to say, the game isn't a bad idea in it's entirety, but it would need several other unique games added in, and would require becoming a compilation. As is, games of comparable level have been released as free-ware, and there are other games available from Yahoo games or Popcap that bear similar qualities, yet have better animations and more depth.
As for a tester, I have no idea where you can find one. I'd do what you're doing now, but perhaps on a site with a bigger userbase. Something like Gamefaqs, though you will find obnoxious people there, too.
To me, the game doesn't seem worth very much. It gets old pretty quickly, IMO, and luck can add a whole lot to solving the puzzle quickly. I think of the game like Minesweeper, but it's too short to play on the low number modes, and there's a little too much to keep track of at once on the higher numbers, if you want to play without hints. I compare it to minesweeper, because the same type of logic-based puzzle gameplay. The difference is that minesweeper just entertains me for a longer extent of time.
With UI, you should implement mouse-compatible number selection, just so people can play it like so. Also on the opening screen, you need to tell people to click one of the two choices in the option bar. As far as the the graphics go, you could turn it into a childs game, with something more friendly, like baryard animals. The idea could be that a farmer would have to buy and order certain animals to properly fit into his barn. Using images instead of numbers and naming the salesmen Poppy and Rose could add characterization into the game, similar to the smiley face in Minesweeper, it helps to attract others.
Like I said, as far as value goes, it really isn't worth much to me. I can see it being of some value on an IQ test or something. It needs more to be of value otherwise, I think.
I don't know what you mean about playing the game on a network, though.