Forcing a refund with Paypal can be done but not in all situations. It can depend on whether your Paypal account is hooked up to a credit card or bank account. If using a bank account most transactions through Paypal can take up to five weekdays (working days). Thus allowing a decent amount of time to cancel the transaction, meaning a cancellation as opposed to a refund.
Some, not all credit card companies may consider electronic transactions from one source to another to be immediate, if the proper funds are available at the time of the actual transaction. This would leave a decision for refund up to the payee, not the payer. This is where registering a Dispute through Paypal may be required. More than not Disputes normally go in favor of the payee, especially if the payee is a well established business.
Also, some businesses have a strict policy on no refunds. Paypal will normally abide by the company's (payees) terms and refused to offer a refund regardless of the situation.