I'm sorry to hear that you received conflicting information when you contacted my team about this, but I will do my best to clear up what you can do. While we do not have any tools available that could accomplish exaclty what you described automatically, you could get pretty close using our Auto Relist Profile feature.
The closest you could come to what you described using our tools would be to post your fixed price items with a certain quantity using the Good til' Cancelled duration, then set up an Auto Relist Profile that would automatically relist the item once all of the items have sold.
If you would like to do this, you would want to create an Auto Relist Profile that has "All items have sold" selected as the condition in the "I want to Auto-Relist If" section and then apply that Auto Relist Profile to your Good til' Cancelled listings you would like to relist in this manner.
If you had 10 of Widget A available and you were posting your initial listing with a quantity of 5, you may also want to select "Auto-Relist a maximum of 1 times" or "Auto-Relist until Inventory Quantity has gone below 1" in the Recurrence" section to avoid relisting the item again once you do not have any left to sell.
Another option would be to simply post your initial fixed price listing for Widget A with a quantity available of 10 and it would then remain active until all of the items sell or you end it manually. If you were to take that approach, you would not even need to use an Auto Relist profile.
Unfortunately, we do not have anything in place that would allow you to automatically add the the quantity available in the listing as each individual item sells.
Since you mentioned the idea of wanting to post a new listing once each item sells, I'm also inclined to mention that eBay no longer allows an individual seller to have more than one fixed price format listing active for a single product. You can read more about this policy on the following page of eBay's help index: http://pages.ebay.com/sellerin...telistingpolicy.html
I hope this helps. If you have any additional questions about this, please feel free up update your existing support case on this topic and ask for me by name.