Bulgarian term (edited): ������� ������, ������������ �������� ������

Advance Payment Guarantee insures the obligation of the seller to return the advance payment in case of failure to supply the goods ....
or
Bank guarantees to the buyer returning the downpayment, if the seller will not deliver the goods, paid for. Guarantee is issued before the advanced payment is made, but it will come into force after the payment has been received by the seller.