You might also fix your own car and tinker with it because it is fun to do so. If you have problems you move on to another supplier of the service - just like Open Source. Another interesting parallel is that of accreditation. Most people do not know a good car mechanic from a bad one. Most non-computing people don't know a good software engineer from a bad one.
Car manufacturers accredit companies and individuals they feel offer a high enough standard.
They put their own name on the line to guarantee the quality of those they certify. If an official Ford dealer lets you down, you blame Ford, not just the dealer. In the Linux world you have things like the Red Hat Certified Engineer and you have approved support partners. If you happen to know a good cheap mechanic then you can use them. People who find a good local car repair will often remain very loyal to it.