But Docan gave me all the numbers before I even when to the PayPal page. Once I pay for the transaction, I have never got any additional fees. It's very clear how much it will be to get those cells to my door.
I do not get what you are saying.
It's pretty well established that if a store advertises something at a certain price, and then doesn't have that item when you walk in, or adds additional charges when you try to purchase it, that's a shady business practice. If they do it with the intent of getting you to buy another, more expensive item, then it's called bait and switch (not the situation in this case).
Sales tax is a known, statutory cost that's added to every bill by every (legal) seller. It may vary between jurisdictions, but you know about it going in. You don't, however, expect to go into a grocery store and see a 5% charge for paying for your groceries added on top of your bill. It is not a standard business practice for Chinese sellers, as illustrated by my experience with importing machine tools and buying stuff off AliExpress (same company and offers same payment services as Alibaba).
But when you buy these batteries, you're not buying them off Alibaba. You're sending payment to the company and they ship the cells from a US warehouse. So the additional charge just for paying your invoice is at the discretion of the company. It's not a statutory or consistent charge across sellers (i.e., common business practice).
Side note: Years ago, VISA used to have a clause in their contract with sellers that prevented them from charging an extra fee if someone chose to pay by credit card, rather than cash in parts of Asia. I've forgotten the name of the clause, but a colleague mentioned it after going on vacation in Nepal with someone who worked for VISA and brought it up when a seller tried to add a surcharge. Now, it seems common for some sellers to add a charge if you use a credit card rather than paying cash (gas stations are an example).
