Earth moving fabrication is not always required, but when it is choose an experienced fabricator. Earth moving equipment is a huge investment. There are plenty of pieces of used equipment for purchase. However, sometimes there is a specific job that needs to be done and custom equipment needs to be built. Make sure you select a company that understands the job you are trying to accomplish. They need to understand how you do your job not just how they do theirs.
When you do choose a used piece of equipment find a company that can help you. A lot of fabricators will also deal in used pieces. The know how to refurbish them and they know how to appraise the quality of the machine. It is a more secure way to purchase used equipment as well as construct new equipment.