How does return shipping work when it's "free"?

[taffgiraffe]

I'm unclear how return shipping works when it advertises it's free ("Ship for free by...."). If I ship it in a bubbled mailer, it'll be paid for the same? Even if it's more expensive than what seller used? They used an envelope bigger than what should be excepted and only cost a little over a dollar. Will printing this "free" label cover the expense? 

[klhmdg]

Free return shipping is paid by the seller.

The label is free to the buyer doing the return but the seller is billed for the cost of the return shipping.

[taffgiraffe]

Does the seller choose the size or weight of package beforehand? Or is that done after or later?

[klhmdg]

No need for the seller to choose the size and weight of the return package.

From the Return Shipping page -

When the buyer is returning the item to you, the cost of the label will be charged to your account once it’s scanned by the carrier. We may ask you to accept a billing agreement to authorize payment for these kinds of charges. If the buyer doesn’t use the return shipping label, you are not charged for the cost of the label.

Any time you use an eBay return shipping label, eBay will automatically select the cheapest return option for your item.

In some instances, return shipping charges are estimated rather than based on the actual weight of the package. These charges are based on rates negotiated by eBay, and are typically less than what you would pay the carrier for the same item.

If the expected shipping charges exceed the expected refund or the refund value of a replacement or exchange, an eBay return shipping label won’t be available.