hello

i incorporated a PayPal button into my website and getting the transaction id the amt entered after the transaction is complete. this information i am storing and am displaying to same client, his balance and the amount he stored in his account in our database. till this point everything but this transaction id and amt is being sent to us using the GET method so if a person comes to know about the url being sent , he/she may maliciously change his/her transaction details. Is there any solution to this , plus i was thinking about using the PayPal's return and rm=2 HTML variables , which sadly are not working . Or is it possible for me to pass on some id to paypal when the transaction is being initiated from my site and it is being sent through the PayPal and i receive back the same id when the transaction is completed and the page is redirected to my page.
i am using sandbox