Over the years, we developed a network of other shops that we refer jobs to if they are outside our scope of service. As an example, we sometimes get asked to do jobs that require a rotary engraver. We don't offer rotary engraving, so we pass those leads on to one of our local shops that does rotary engraving. They reciprocate when there are jobs that our shop is better suited for.
I have found that the best way to get the relationship started is to contact the owner of the shop with a job you already have in hand but don't have the capability to do. Let the shop owner know who you are and that you have a job that you don't have the capabilities to complete. Ask if they are willing to help. The answer is almost always, “Yes.”
Set up a time to meet the shop owner at their shop with the job in hand. Spend some time talking with them, getting to know their additional capabilities, and letting them get to know you. After you take two or three jobs in person, you will have an idea of their quality, pricing, and the way they conduct business. If you've had a good experience, it's a safe bet your referrals will too.
People generally like to reciprocate, and you'll find that some of these shop owners will send referrals back your way. The shops that don't end up reciprocating don't stay on our referral list. It's the old, "You scratch my back, I'll scratch yours," principle.
—Mike Westbrook, Mile High Laser Engraving