Bitcoin transactions will never be reversible or refundable. Once your transaction is complete, you receive a notification and that is that. One will always be recieve the goods you bought from a company when money transaction is complete. If by one way or the other, you do not receive what you paid for, then you can trace whatever you bought with your transaction ID. Moreover, you should be aware of the authenticity of the company or shop you are dealing with in order to avoid being scammed.