Can I refund an order directly from Magento?
Yes. In order to do this you have to create a Credit Memo on the Invoice and then click on REFUND, (not on refund offline). Please keep in mind that this is a PRO only feature.
I'm using PayPal via Sage Pay and the cart contents are not transferred to PayPal.
This is correct, its a known issue that Sage Pay is aware of, we can't do nothing about it but keep in mind that unless you disabled it all cart lines are transferred to Sage Pay on every transaction.
Can I defer a payment and capture money after for example, I have the products ready to dispatch?
Yes, you can, our extension implements DEFERRED and AUTHENTICATE payments, you can choose between them at any moment, keep in mind that these affect all transactions and you can have deferred on frontend and regular payments, on backend at the same time.
In order to capture the money when using deferred or authenticate payments, you just need to create an invoice on Magento's backend, and the payment will be released for the invoice total, you can create multiple invoices.
Read more on different payment actions here
Does Sage Pay Suite support Multishipping Address Checkout (MAC)
Yes, it does. A few considerations though.
When DIRECT protocol is used, a transaction is created per every order, skipping 3D secure checks.
When SERVER is used, only ONE transaction is created and the subsequent orders will show a label like "This transaction is child of ..."
FORM and PAYPAL via SAGEPAY do not implement MAC Checkout.
I'm behind a proxy
Check this https://gist.github.com/centerax/5713820
Can I use surcharges with PayPal?
SagePay protocols do not allow surcharges to be added to PayPal transactions. If you require surcharges on PayPal transactions, we recommend to contact PayPal directly, as this functionality should be available in your PayPal account.