Yeah, Ebay is great for this. I was able to replace the mainboard on an older LCD TV I was gifted years ago. $50 for a used one, exactly matching model#. 15 minute replacement job, 0 wasted televisions.
It does depend on the car part. There are a lot of low quality fakes on ebay, which won't either work, or will break quickly, and finding information with which to sort through which are good and which are not is a task in itself.
The consequences can be even more serious if you're looking for aircraft parts. A few years ago there was a discussion about Chinese made crankshafts for Corvairs on HackerNews, covering this exact issue: https://news.ycombinator.com/item?id=18788861.
Fixing household white goods where a failure could result in a bad load of laundry or burnt toast is very different from aviation where utmost care must be taken with regard to maintenance, overhauling and repairs.
Even in cars, you gotta figure, is the part critical? (brakes, steering) or non critical (wipers, seats, heating/ac, etc).
For sure. I was pointing it out more for interest's sake than as a serious point of comparison for fixing your washing machine. Still, even there I'd probably be relatively careful, because flooding your kitchen isn't so much fun (bitter experience speaking there, although fortunately the kitchen is at ground level and has a concrete floor under the lino so no serious damage done).
You’re right that there is a possibility of somewhat disastrous results, but in my experience it’s not the motor or high voltage electrical that goes out but a plastic part, an on-off switchbor or a sensor.
Yes be careful, you could get an electric shock photograph before you take things apart and read instructions before putting things back together.
I was quoted 600 for a whole system part of a car (dubcomponent wasn’t sold separately), the actual necessary used sub-part was 50 on eBay.