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As the owner of any small business, you have to play your cards right with contractors. In order to draw in these contractors offer them a cash payment or their hourly rate for the type of job you are looking. In this case, the independent programmers should be offered their hourly rate for the job you are looking to complete. In order to bolster the loyalty and relationship, it is important to get to know the person on a more personal level, by meeting in person or talking over the phone. After which, praise them on a job well done, and offer them a chance to work on future jobs when the chance arrives. Most people, will work continuously as a contractor for one group or company, if the experience working for them was a good one. It's simple mutualism at its best.
Please let me know if you have any more questions. I am a student from MIT, and i would be happy to answer your questions. I promise 100% on all of your assignments! Take Care!