In our lending platform, the borrower locks the collateral in a multi-signature address created for that specific contract using his own enthropy. This escrow address is a 2 out of 3 multisig. Lender has one key, borrower has the second, and Hodl Hodl has the third in case a dispute arise and a resolution must be taken by the admins. Meaning that NO party on its own can move the BTC locked in escrow. Usury is not possible in an unregulated global free market like ours, where both parties agree on all the terms of the contract. If a lender asks for a too high APR percentage, they will just don't get any borrower. And if a borrower wants to pay a very low APR, they just won't find any lender. A contract occur when both parts find a match in the middle.