The truth is we will be charging the different rates from the above persons .
There is a difference between Repo rates and repo margins look to the trade below
Diagram 1 - start
Trade details:
Principal: $10,000,000 Bond price: 100% Repo principal: $10,000,000 Repo rate: 5.00% Actual/360 Term: 7 days Borrower Lender
Diagram 2 - maturity
Trade details:
Principal: $10,000,000 Bond price: 100% Repo principal: $10,000,000 Repo rate: 5.00% Actual/360 Repo interest: $9,722.22
As you have noted the repo rate is same at 5% without any credit risk , as the collateral is exchanged at par value and there is a interest of 9,722.22 for 7days
Now Repo margin
Sincerely , the lender of the money does not care if the bond price is falling IF he is damm! sure that he will receive his $10 million with interest amount , Because he has to just return the collateral to the borrower and receive the payement.
The question arises that What IF the borrower defaulted and by the time we went to the market to sell the security the market value of the collateral security has drop , so the risk starts from the risk of borrower’s default.
According to Wikipedia
While classic repos are generally credit-risk mitigated instruments , there are residual credit risks. Though it is essentially a collateralized transaction, the seller may fail to repurchase the securities sold, at the maturity date. In other words, the repo seller defaults on their obligation. Consequently, the buyer may keep the security, and liquidate the security to recover the cash lent. The security, however, may have lost value since the outset of the transaction as the security is subject to market movements. To mitigate this risk, repos often are over-collateralized as well as being subject to daily mark-to-market margining (i.e., if the collateral falls in value, a margin call can be triggered asking the borrower to post extra securities ).
Either you can go for a margin call in the middle of life of the repo aggrement or you can go for an Haircut in the starting of the Aggrement itself based on the probability of defualt and chances of security to go down in the value.
Now the answer to your question:-
Client A: - He will get the repo rate of 5% on 10 Million
Client B:- He will get the repo rate of 5% on 9 Million ( After haircut because of counterparty credit risk) but has to pay the same 10,009,722.22 at the end . Thereore the effective rate of borrowiing of B is 11.219% (cosidered for whole 1 Year than 7 days for easy calculation) will be higher that A.
Hope This help!
Still any doubt please feel free to ask