I've always been outspoken against price shopping for parts to repair laptops. You want to arrange by lowest price – you'll get precisely what you bargain for, and eBay & Amazon are two of the worst cespools when it comes to purchasing repair parts.
Today I'd like to use the example of Macbook glass. This was brought in by a customer hoping to save a few bucks. We charge $100 in labor to replace the glass, but $150 with our part. He got this for $19.99. Here are a few of the things you get along with that cost savings of $30.01. We repair the glass on A1278 Macbooks and also sell the part for those so inclined to repair it themselves.
You are giving your customers excuses to bargain with you. You are giving them reasons to say “I'm not happy with this – I'm not paying.” You're giving them reasons to leave a bad review.
You're turning a beautiful, $1200 laptop into a piece of shit. The very part you interact with on a regular basis is tainted in a manner that, even if it is subtle, makes it shittier to work on.