You're forgetting the convenience factor that the payment service creates in the market.
Let's say I sell trinkets for $10/each online. They are nice trinkets, but no one really needs my trinkets. No one is going to send me a money order in the mail for a single trinket for $10. Basically, there is no online market at all, unless I can make it easy to buy my product.
But if I charge $11/each and accept Paypal (or credit cards in general), I now have a real market for my trinkets. People like my trinkets, so they will gladly click on a Paypal icon and send me the money that way.
Now my trinkets are somewhat popular. A couple times a year someone stops by my workshop and asks to buy a trinket in person. I still charge them $11.
Let's say I sell trinkets for $10/each online. They are nice trinkets, but no one really needs my trinkets. No one is going to send me a money order in the mail for a single trinket for $10. Basically, there is no online market at all, unless I can make it easy to buy my product.
But if I charge $11/each and accept Paypal (or credit cards in general), I now have a real market for my trinkets. People like my trinkets, so they will gladly click on a Paypal icon and send me the money that way.
Now my trinkets are somewhat popular. A couple times a year someone stops by my workshop and asks to buy a trinket in person. I still charge them $11.