Every listing has two buttons. Add to Cart keeps the item while you carry on browsing. Buy Now takes you straight to checkout with that one item.
Why your cart is split by seller
Items on eBuy come from individual collectors, not from one warehouse. Each seller packs and posts their own parcel, so checkout groups your cart by seller.
This decides what you pay for shipping. One seller means one parcel and one shipping charge. Three sellers means three parcels and three charges, even if everything would fit in one box.
So buying four items from the same seller costs much less to ship than buying one item from four sellers.
What you pay
Item total, plus Shipping & Protection. Nothing else. The platform fee and payment charges come out of the seller's side, not yours.
If your payment fails
Nothing is charged for a failed payment. The items are held for a few minutes before you can try again, so that a half-finished payment cannot sell the same item twice. Wait for the time shown on screen, then retry.