Why a large order arrives in pieces
Buyers ordering a big amount for the first time often expect a single trade and read anything else as a problem. It usually is not. Sellers hold stock across more than one character, a single stack of coins tops out at a little over 2.1B, and both sides generally prefer a handover that can be stopped partway if something looks wrong.
So the normal shape of a large delivery is several trades in one session, sometimes from more than one character. That is ordinary, and on its own it is not a warning sign.
What can slow a handover down
Newer accounts, and accounts that have not established much history, can face trading restrictions that do not apply to established ones. The details change over time and are worth checking against current game information rather than taken from any guide, including this one.
The practical point is that this is worth knowing before you order rather than discovering during a handover, while a seller is waiting. If you are buying onto a fresh account, say so in the order chat early — a seller who has handled it before will tell you what to expect.
Arranging the handover
Agree a world, a meeting place and a time in the order chat before either of you logs in. The Grand Exchange is the usual choice because it is central and busy, and a busy location is a better place to stand than an empty one.
Then work through the trades. Check each one as it arrives rather than at the end — it is much easier to raise a discrepancy on the second trade of six than to reconstruct what happened afterwards.
Confirm once, at the end
Confirming delivery releases the payout and closes the order, and it cannot be undone. So confirm when the whole amount has arrived, not when the first trade has. A seller asking you to confirm partway through is asking you to give up the only leverage you have while they still owe you something.
If a handover stalls halfway — the seller stops replying, or the rest never comes — that is precisely the situation the dispute button exists for. Do not confirm and hope. An unconfirmed order costs you nothing to leave open a little longer.
When it spans more than one session
Very large orders sometimes cannot be finished in one sitting, particularly if the seller is sourcing across characters. That is workable, but agree it explicitly at the start rather than discovering it at the halfway point, and keep the arrangement in the order chat where it is recorded.
The short version
Confirm the order when the whole amount has arrived, not when the first trade does. Partial delivery is the exact situation the dispute button exists for, and confirming early is the one move that closes it off.