I think it might be better to create a tracking/data entry sort of app separately from a marketplace app. Perhaps you could import the data from the app that has the information regarding feeding, sheds, etc., into the marketplace app, rather than having them combined?

I was really liking the sounds of this app from everything before "among other things". I'm currently using an app that's specifically for dogs to track my BP's eating, sheds, age, and other things. It's a little awkward because the only options they have are "milestones" and "diaries". Obviously, since dogs are supposed to eat every day they don't have a feeding tracker. For snakes, however, that would be lovely. So, I would gladly endorse an app that offered the services you mention as far as husbandry and record keeping. I would definitely be willing to pay $.99 or $1.99 for such an app.

I personally would not use a marketplace app, especially one with bidding. I don't feel comfortable bidding on animals. That's just me, though. Also, I think it's way too complicated to have so much data in one app. I would rather not rely on one application for storing all that information, especially when money is involved, to be the place I put all data about my animals.