Milestones are how a deal that takes weeks gets paid without either side going first for the whole amount. The questions people ask are always the same three: is the money really there before I start, what happens to one milestone if we disagree on it, and can the other side change the split halfway. On iEscrow the answers are: yes, it is frozen alone, and no.
The mechanics
Funded
The paying side funds the whole amount once, before the first milestone starts. There is no "fund the first stage and we see". The receiving side sees the full amount locked.
The split
Each milestone has a percentage; they must add up to 100%. Written before funding, visible to both.
Delivered
The receiving side declares a milestone delivered. The paying side confirms it (or, for product and service trades, lets the window pass, which releases it: silence does not hold a delivered stage hostage).
Released
On confirmation, that milestone’s share moves from escrow to the receiving side’s balance. The rest stays locked.
Disputed
A disputed milestone is frozen on its own; an arbiter decides it on the evidence. The other milestones continue. A milestone decided against the receiving side refunds its share to the payer.
Terms
Once funded, the milestones are the milestones. Neither side can add, remove or re-weight them unilaterally. If both agree to change the plan, that is a new agreement, not a quiet edit.
Tying a milestone to an inspection
The most useful milestone in an import deal is the one that releases on a passed pre-shipment inspection. The inspection is yours to arrange; the milestone's condition is the report. The money is funded before the inspection and released after it, so the supplier has every reason to pass it and no leverage to skip it.
Write the condition of each milestone so that a stranger could judge it: "inspection report by X, AQL 2.5, dated before shipping" is a condition; "when it looks fine" is not.