I had similar quality issues with a local supplier. It happened to be mostly on starters also. I let them know of the quality issues. They said no one else in town is complaining. They did not address my concerns and we buy some were else. I do not like to have to do a job twice. It happens from time to time but to me quality is the key. I want my customers trust and feel like I will do what is needed to earn that. We do not install customer provided parts unless its a wiper blade, bulb or maybe a hard to find part on a classic car. As far as parts matrix goes well every shops overhead is different. That should dictate your matrix not other shops and what they charge. You need to charge enough to stay open pay the bills etc.