Selling: too many people, too few items!?

I'm really in a sticky situation right now. I'm selling a few popular saddle pads in order to buy a more expensive one that I need, and there are so many people interested. I've been getting back to everyone and unfortunately don't even know who responded to my ad first. But basically, there are a couple people ready to pay right away, and I don't know who to sell to! Some people are making offers and some are saying they're ready to pay now, but want to make offers that I haven't heard yet. Others have so far just asked for shipping. Who the heck do I sell to?! I also need to figure out sme sort of policy so everyone knows how it's going to work from now on. Thanks!