This is getting into another issue again.

Although there will always be some cheap and nasty generic parts on the market (just like you can buy cheap clothing that falls apart, although some branded stuff does too ), there's little doubt manufacturers have used the old 'genuine parts' slogan as a deliberate marketing tool because they make a decent margin on spares. This isn't a whinge btw, if that's how they can add to their bottom line, fair enough.

The difficulty for the average consumer is that as cars have become more and more complex with the proprietary systems Timbo mentioned in his post, it is harder and harder for people to wander into their local Repco or Autobarn and feel confident that the generic part on the shelf will be compatible.

So you either spend a lot of time in places like this learning and looking for ways to cut corners on cost or you just bend over for the dealers, take it like a man and get on with life with a lighter wallet.