Misalignment of objectives.
You want cost assurance, quality and reliable estimations.
They just want to get paid.
Fixed-fee projects seem like the safest bet but they work against you.
All you’re really doing is pushing the risk onto the development company.
This will allow you to strong arm them of course but in the end, both of you will lose.
You may get the project delivered, but corners will be cut and it will be noticeable.
Instead, really spend the time to determine the business value of your project.
Instead of looking at it like a 100k expense, figure out how little you can spend before you could have a revenue producing customer.
Make sure what you are building is something customers actually want and will pay for.
It changes the whole equation and you find out early if you have a good development partner or not.