I just checked several of your listings and none of the ones I looked at had multiple numbers listed. ie they where all one item only available. It looks like you possibly sell that one and then relist once sold ????

When listing or revising a listing there is a check box two thirds of the way down the page to list multiples of the same thing. If you have six beer mat sets, you set the quantity to six. If you combine postage, once you show more than one of the same item available, the postage option changes to allow cheaper postage should one customer buy more than one of the same thing. ( great for christmas when people buy multiples of the same thing to give as gifts )

It is this simple feature that I use to manage my stock as per previous post. All up I have around 2000 listings on three selling accounts and it is working no problems with that number of listings.

Like all things on ebay, the simpler you can keep things, the more time you can spend actually selling and packing stuff, rather than chasing your tail on extra steps that unnecessarily complicate the process.