Paypal Standard and Paypal Express are the payment methods integrated in the CrystalCommerce admin in order for your customers to finish processing their online transactions on your CrystalCommerce website.
There are few differences that you should know:
Standard can be setup in your admin using your Paypal email account but in Express, you would need to create a business account. The transition from personal to business account is free and even offers additional discount for our CrystalCommerce users.
In Standard, you have to set up your Paypal API to refund orders in the admin instead of logging in to your Paypal account. This step is not needed in Express and you can still refund just like in Standard.
The two Paypal services offer the same advantages and security. In fact, if you do not have a Paypal account you can still purchase and pay using your credit and debit card on both payment methods. The only real difference for your customers is the checkout flow. In Paypal Standard, your customer completes their check out and will be directed to the Paypal website. In Paypal Express, your customer go to the Paypal website first to approve the purchase and they go back to your website to finalize the order.
Internally, the process is much more complex. The checkout in Paypal Standard is completed on Paypal site and your store will rely on the success or failure notifications from Paypal. This is called Instant Payment Notification or IPN. The checkout in Paypal Express does not rely on IPN since the order of the check out is different and the client will end up on your website again rather than leaving it.
Historically, either payment method has been effective on client websites and has not been an issue but only a matter of preference. So, go ahead set one up based on your preferences.
To learn more about two additional Payment methods try these articles:
How to setup your Authorize.net account in your admin
How to setup your Beanstream account in your admin