transferring bitcoin is irreversible so if he use it as payment online he should do it accurately. Besides, it is faster and easier using bitcoin as payment with no hussle at all. This is one of the disadvantage of using bitcoin, other payment online can be recover if you accidentally transfer it in a wrong way because they are centralized unlike bitcoin. But if you are using some bitcoin app that has customer service maybe there is a possibility that you can recover your lost bitcoin (I am not saying the one that sent in wrong btc address.
Lol, I think you guys are just confused. This guy is a merchant and he's looking for a safe payment method. And from what he said, he wants a method that is irreversible and that doesn't seem like a good idea to me.
If he needs a method that is irreversible then he can make us of Bitcoin but a lot of people are not going to like that. This means that he can sell a product having defects to someone and there will be no way for them to return the product and asks for a refund. No one is buying that.
If you have your merchant site, the basic way for accepting payments online is through credits and debit cards. Majority of the merchant sites I see these days are accepting credit and debit card payments and I think it makes thing more easy for your customers. You may choose to accept other methods of payments. There are people who accept eChecks, and mobile payments are also another popular methods that are being used.