This is more feedback than suggestion, because I doubt you can fix someone elses mod, and it's probably some complex metadata issue (like trying to list a golden bag or something)... Anyway, just fair warning, I put a dolly with a spider spawner on it so people could buy it if they wanted to create a ender io spanwer (or draconic or whatever) as broken spanwers are useful, and yet being a functional vanilla spanwer it would be helpful for people who hadn't had the resources to do either more advanced spawner. When I finished the market sell it listed as a regular unbroken diamond dolly. I cancelled the auction and indeed got a regular dolly back, missing the spawner. I guess it doesn't matter. I'm okay on spawners for now. My guess is I could break the spawner, and list that, or list one of the other spawners (stablize it and/or turn it into an enderio spanwer) then list that...but I know everyone doesn't like to be handed the end product and would rather do some of the work themselves. At any rate, I guess I can't sell vanilla spawners, and hopefully anyone who reads this will know better than to try now.