Well there isnt any sniffer that will display the Packets before they are encrypted for every Game. But of course, you would be able to create your own Packet Sniffer / editor for your game but for that you need development and Reversing skills. Since (i think) you dont got any development / reversing skills it would be useless to explain how you go for this. But if iam wrong and you got Reversing and development skills, you should take a look at this tutorial:
But remember, even if you are able to create a Sniffer / Editor, you cant do everything you want.
Like you wouldnt be able to send a Packet to sell a special item, while you dont got this item.
The Server would see that you dont got the item you are trying to sell.
PS:
Here is one way how you would be able to inject code without a dll (c++ / asm) (
German):