REO Experts, Please help! Do we have to use seller's lender?

We made an offer on a bank owned foreclosure townhouse, we\'ve already have pre-approval letter from Bank of America, the approved loan amount is much higher than the asking price. But the listing agent said we are required to have approval from seller\'s perferred lender, so we called the guy, a loan officer from a different Bank of America branch, and he told us not only we need his approval but we also have get loan directly from him. Is this normal or even legal for REO sales? We are also required to use seller\'s preferred Escrow and Title companies.

We don\'t have any experience in REO sales, please provide your advice, we really appreciate it.