what would be the best solution to arrange items on Magento?

my client is asking me to arrange items freely. Let's say I have five items. Item 1,2,3,4,5. My client wants to move item 5 to item 1 and item 4 to item 2 and so on.

I have never seen such feature before. I am not even sure how to implement it.

What would be the best solution??

If you go to the Products tab when editing a category you can choose the order products are displayed in - this is the "Position" ordering on the frontend.

Greg is actually not entirely correct. When you go to a category within the Magento admin, then click on the products tab for that category, you'll see a listing of all the products, and there will be a "Position" column where you can enter in numbers for ordering.

On the frontend, you'll see that there is a "Position" sort order option. That's what this is for. There is no "Bestseller" ordering.