We study how intermediaries transmit idiosyncratic funding cost shocks to consumers using a field experiment in the U.S. auto loan market. A subprime lender randomly varied the interest rate offered to dealers. Dealers could profit by marking up this rate to set the borrower’s APR. A 1 ppt increase in the offered rate reduced loan take-up by 14%, and the pass-through ratio to the borrower’s APR was 0.89. Dealers’ proposed margins were largely insensitive to the offered rate, revealing that sophisticated intermediaries transfer cost shocks mechanically, not strategically, highlighting a key micro-level feature of the transmission of interest rate changes.