The builder is looking for a commitment. That means that they have pulled your credit report, taken a FULL loan application and have done some type of review.
The commmitment will list all the conditions of the loan.
Why would a builder want this. The same reason you as a home seller would want this, along with a large deposit - because they want to make sure that you qualify.
What happens if the rates increase in the 9 months? The lender will put you into another program. I'm SURE that this is written in the contract. You are NOT locking into a interest rate. The contract would state, "prevailing rate at the time of settlement". In addition, it will state that you will work with the lender to get a loan.
READ THE CONTRACT. The builder isn't being unfair. They are spending $$$$$ to build the home on a promise and your deposit. They want to KNOW that you qualify.
If you want to lock into the interest rate, I know that lenders are offering up to 1 year "FREE" interest rate locks. You pay a deposit up front, usually one point and when you settle you get the full deposit back. Usually if rates drop, you can float down to the lower rate one time. for free.
In regards to the "mortgage broker" who states that a construction loan is safer: under a construction loan, the buyer actually owns the house under construction. The builder only gets paid for work done. However, the buyer is on the hook for every penny- so if the house is delayed or etc, the buyer pays interest carry every month. NOT A SMART WAY TO GO in this case.
In regards to the lender that says that a loan commitment is like a loan pre-qual and that he just writes them for 'fun'. This type of lender will burn you!!! I promise that the builder will hold you to the contract, no matter what. This type of BS is the reason that builders want you to use their "approved" lenders so that when a letter of commitment is given, EVERYONE (you and the builder) is both protected. Shame on this lender!!