I already purchased. Why Android market try to charge me again for re-download?
This type of problem is mostly caused by the change of primary Google account in your phone.
In most cases, it happens by entering new primary account email after factory reset or getting new phone. As a result, Android market recognizes the phone owner as new user and cannot verify the previous purchases.
Please see the following documentation for more information.
(If you decided to fix the problem by factory reset, please make sure you do extra backup for the installed apps.)
In Android market, our role is limited to product support and all the sales and distribution activity is tightly controlled by Google with strong customer protection policy. Therefore, the customer information we can see is very limited. However, there's still some part we can help.
If you need help, please feel free to contact us with your 15 digit Google order number. We will be more than happy to assist you.
The google order number can be found in in purchase receipt email and it is the only way for us to find your order.