My Method has been used and tested by my self and it works.
E.g You have a product called "Watch Tv Online"
I would sell this Product In my shop and have a quantity of 1000.
I then would create a Fixed auction and the description of the product shall be the same, the only difference would be is, I will Click on the Shop Builder. ( The shop Builder is the "S" Button on the toolbar)
When you have clicked on the Shop Builder you will Build a link to a item, Type in the item number for the "Wacth Tv Online" remember this is saved in your shop. You can browse for a Image and write in the description.
Just click continue and add html to my listing.
You will then see a Link in your description taking you to your shop to buy the product. This will be at the bottom of your listing.
At the top of your listing you can tell your customers to buy from your shop by scrolling down.
Please remember any products you have always create a Shop format for them products in 30 day you are guaranteed to sell each product in your shop atleast once, you will not make a loss and your shop visibilty will increase.
Once your Shop Visibilty increases it will be easier to find customers and your Fixed auctions will benefit.
Enaam & Tawfeeq