I am coding my website using Codeignitor and MySQL. Users need to create a new account to use my website. Every user has a unique ID along with other information saved in the database. I plan on using an online payment service such as PayPal or Google Wallet.
However, after a user makes a purchase, how do I match that purchase on the online payment service (ie. Paypal) to the user in my database, so I can render the appropriate service to that customer?
For example, if a user makes a purchase using the PayPal button, I'll see a record of that purchase on my PayPal account. But how do I know which user of mines in my database is the one who made that purchase listed on my PayPal merchant account? Do I just have to trust that user's information on PayPal (First name, last name, etc) is the same information he or she entered on my website?