Is my mechanic a scam artist? Or is this normal?

[Mama Hip Rockets]

I ordered a car part that seemed suspiciously high ($125 for a used, unpainted driver side mirror, plus labor and paint job on top of that), and did some research and found that the part was much cheaper online (found the mirror for $36 by doing a quick google search).

I called them and asked them about it. All I said was that the price seemed a little high, and I told him the website that was selling it much cheaper. I asked him if it would be possible for him to order it online, and the mechanic got his panties in a bunch and said I was accusing him of lying. Then he added (without any prodding by me), "I added maybe, MAYBE, $20 onto the price." That seems like quite a mark-up (around 20%), especially when he can't even remember the exact amount.

Are mechanics supposed to make their money from the labor, or is it normal for them to mark up the price that much without telling you? The thing that bothers me the most is that we have been going to this mechanic for a while, and normally the service and prices have both seemed reasonable.