The information in this answer is general information and is not intended as legal advice, nor do I intend to create an attorney-client relationship with any reader by answering this question or otherwise contributing as a member of Trulia.com.
If you are making an offer on a distressed property, you may be required to provide proof of funds before your offer can be considered, since those are usually cash sales. With very high-end luxury properties, the seller's agent may ask the agent representing the buyer to "pre-qualify" his/her client. This involves relaying some general information--mainly regarding employment, to ensure that the person requesting the showing is a serious buyer who could actually afford to purchase the property., and not just someone curious about an expensive house.
Aside from the above situations, the details of your personal finances should remain between you and your lender. Understand, however, that your real estate agent has a fiduciary responsibility to you, and may not share personal information about you--of any kind, financial or otherwise, without your permission. This confidential relationship does not end when the sale has been completed--similar to the doctor/patient and attorney/client relationships. Although we're talking about real estate transactions here, as you can imagine, there are many different issues involved in buying or selling a home--both financial and personal, that should always remain confidential. That's why it's very important to work with a real estate professional with whom you can develop a comfortable and trusting relationship.
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