It has been said sometimes that a Bitcoin transaction can be cancelled or reversed using for example double-spend.
Is it still possible? If Yes, how? If No, Why?
Especially when you sell services and goods and accept Bitcoin payment, you are worried about this.
So it should be a good idea to discuss this topic.
I know that you could not cancel your bitcoin transaction once you confirmed or accept it because it will be delivered instantly, but if you have a slow internet connection the funds that you have send will be cancelled.