The cost depends on you arrangements with the escrow agent or bank. As a Developer it is for you to negotiate.
From the client's point of view it gives him confidence that his money is protected until he gets what he is paying for; the money is released in stages. If a Developer goes under the clients can prove what they have paid for to date.
Its not a question of trust it is prudent business practice which is common in countries which have no system of bank guarantees.

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PROPERTY SHOP INC. International Property Brokers
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