http://www.multitran.ru/c/m.exe?t=3889773_2_1&s1=charge

Олег, "to charge TAX" и "to charge one's payment method" это РАЗНЫЕ ВЕЩИ.

http://dictionary.cambridge.org/dictionary/english/charge

https://www.google.ru/search?newwindow=1&rlz=1CDGOYI_enRU590RU590&hl=en-GB&ei=-3iDV9DqFOTR6ASI1rKIBw&q=%22to+charge+payment+method%22&oq=%22to+charge+payment+method%22&gs_l=mobile-gws-serp.3..0i13j0i22i30.5161.6482.0.6826.3.3.0.0.0.0.128.222.1j1.2.0....0...1c..64.mobile-gws-serp..1.2.221...35i39j0i7i30.E0PUEjx5bBk

Можно узнать где здесь идёт речь об "основном счёте"? Как это выглядит на английском языке?

Олег, "original payment method" это данные счета/кредитной карты, которые человек вводит при регистрации, например, на таких ресурсах, как Apple Store/iTunes/Netflix и прочих. Фактически это ваш счёт.

Налогообложение не имеет никакого отношения к этой фразе.

Вот так выглядит эта фраза в контексте:
We would be happy to send you a replacement for the item, since we have more stock available, or we are happy to give you a full refund if you prefer. When we process an exchange, the funds are transferred from your original order to the new order; this is so that we do not need to charge your original payment method a second time. We will ship the exchange order out right away if you choose to have an exchange over a refund.

*this is so - "поэтому", а не "дело в том".

And now, Oleg, please be so kind to withdraw your thumb down ;)

Oleg, this has nothing to do with taxes. When you create an account with a vendor online, they ask you for a PAYMENT METHOD (credit card, money order, check, etc.) Most people choose a credit card, which the vendor keeps on file for future purchases. Here the point is that they are avoiding having to charge something to that original PAYMENT METHOD. Olga's translation is perfect (without дело в том)

Thank you for clarifying, Uly :) Well, I've corrected myself :)

а я уже собирался Вас поправлять, Ольга =)