Accordingly, when inter-dealer transactions are not available, a dealer that effects a transaction in government or other debt securities with a customer and determines the mark-up or mark-down on a basis other than its own contemporaneous cost must be prepared to provide evidence that is sufficient to overcome the presumption that contemporaneous cost provides the best measure of the prevailing market price. In this case, factors that the Board believes may be taken into consideration for a mark-up or a mark-down include but are not limited to:13
2. Contemporaneous inter-dealer quotations in the security in question made through an inter-dealer quotation mechanism through which transactions do in fact occur in that security at prices that are reasonably related to the displayed quotations;