Directly from hud:You have the RIGHT to shop for the best loan for you and compare the charges of different mortgage brokers and lenders.
If this is a shortsale or REO this is done a lot.
You have 100% freedom to use anyone for mortgage and title insurance and don't let anyone tell you any different!
The National Association of Mortgage Brokers has fought this illegal act against major builders and it getting somewhere with it.
The big exception is: If you are serious about purchasing, have your lender do a FULL pre-approval. Submit your documents for written verification; go through the entire application process. Ask your lender to present you with a "pre-commitment" based on only 2 contingencies; a contract and an appraisal.
You will be househunting with a doc in your hand that makes you as close to a cash buyer as possible. You should be working with a Realtor to represent you and be able to present this info to the seller, showing you do not need a simple pre-approval, you already have something much more valuable.