Having been on several sides of this question I hope to give you as much perspective that I can.
Maybe at some point my buddy Alan can chime in to since this is his business as well.
First, getting jobs depends on your experience. Certainly knowing GM, Ford and Chrysler makes sure that you'll always have work just because the dealer population is large enough to provide ample dealers who need temporary or permanent help. Besides that knowing ADP and Reynolds&Reyonolds will cover 85-90% of dealerships.
That being said, don't be afraid to take on new makes, because in the end they are all the same - translating the repair work into something their computer will accept for payment.
With setting up the business there are two courses to take. One is a part time in house processor. That normally invovles a visit a week or so to the store to process their claims at the store. These jobs are usually for smaller stores who can't justify a full time warranty administrator.
The second option is to process the work at your home/office. This can get a little more complex as you'll need terminal emulation software to dial into the dealership, pull up the claims and get them ready for transmission to the factory.
Depending on how you work some people charge by the day (figure a weekly wage per day since you have taxes to pay, etc.) Otherwise the larger national processing companies charge based on claims that are paid (it varies between 4% to 10% for the larger in-house fleet services.)
Let me know if you have more questions, or as always, you can just give me a call when I get back to the office on Monday (800-321-5312).
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** Rob, Editor WD&S **Help is only a message post away!
robc@dealersedge.com