Q: Custom Paypay payment protection I'm doing a PayPal payment system. The steps are:


*

*collect all item & price value that user have chose, through js get from html input.

*redirect to url paypal and add on item and price:
https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_cart&upload=1&business=someemail@here.com&cy_code=USD&lc=US&item_name_1=Black
Gold&item_number_1=1&quantity_1=1&amount_1=$58.00
Question: 
But using this method, user can change the price easily by downloading the page from my site and changing the script. So any protection I can do for this? 
I have 2 ideas now. But I don't think they're good solutions. 


*

*encode/decode the price by server site

*get the price value from sql ...  


A: Use a POST request to send the data and not a GET request (using URL params). Also, use the PayPal IPN notification system to notify you in the situation that somebody tampers with passed values using a hack:
https://www.paypal.com/ipn
