You should take 3 factors into consideration
- Time Frame
- Cost / Budget
- Quality / Complexity of project
Once you have the ideal situation for all of these factors then it should not be too difficult to get the perfect developer / team to handle any of your projects. To explain simply
You can have a great budget and a well written project scope however all of that would be useless with an unrealistic time frame. A good developer plans his time wisely and if he sees you are being too demanding / inflexible with the time after he have provided you with a detailed outline of how long the project would take, he may just skip over it because it causes major headaches down the line.
Cost / Budget
You can have months upon months to complete a project. In other words, time is not an issue for you. The project is well spelt out again with clear instructions on how to achieve what but your budget does not match up to the about of work this project requires. This is a huge indication of problems later down the road as well. A project which is not worth working on generally is frown upon. The cost of living / operational costs must be met for a developer / team for them to think the project is worth working on
Quality / Complexity of Project
This is mainly outlined within your project scope. If you do not have one especially for "large" projects usually raises red flags for developers. You must have a clear (or at least a near perfect) outline of what you would like achieved. It should be something well documented and standard for each developer you come in contact with. Based on your interactions with one developer, you can choose to update your project scope to ensure it is more clearly defined for the next one you move on to. If a developer does not know what he is required to do, you will most likely end up with work you did not expect. The project scope is like a road map a developer would follow to understand what is required of him and of you at times.
Hope this helps you fine tuning your search