On the Ebay module you can also choose a stock limit for the product you will put on sale.
To set the stock limit of the product for sale on Ebay, as you wish, there is a specific field on the settings on our module.
Settings => 2. Listing Settings => Listing Duration
On the Listing Duration tab you have to put a number between 1 and 50 to have a limited stock to that precise number of items for each product.
If you wish not to have a stock limit on your product for sale, you will need to put 0.