I would rather give up the job, than take the chance on a customer supplied part. I trust my suppliers and hope a customer has good luck with what they bought. I won't know, because I won't be involved.
If you have never made a mistake, you haven't done much.
Plus, when said part fails, the homeowner demands that you come back out, free of charge, because they say you installed it wrong.
Please do not get me wrong, I am all for the handy homeowner repairing things that are within his abilities and we all have different levels of abilities, but there are some areas of repair that are not DIY, Gas plumbing, some electrical, gas fireplaces, most HVAC....... You may be able to get it right, but if you miss one "minor" thing, people can die.