Is buying car stuff from eBay a good idea?

You have to make sure you are dealing with a seller who has a perfect or NEAR perfect record. For instance, If the seller has 900 sales and a 100% positive feedback, you have little to worry about.

I have not wasted money on cold air intakes off of e-bay or other wise. Some parts are high quality and others are low quality. Headers are a good example, I own several cars and they all have e-bay headers on them. Only one header has fit right out of four, the others had the holes for the header bolts a little off. Instead of bothering with shipping expenses for replacement, I just modified them to work. The clutch kit (light weight flywheel included) did not contain the bolts needed to match the flywheel. But a more expensive kit from a different supplier may not have had them either. It is a matter of cost, it would have cost me 200 dollars more for a header from another vendor (non e-bay) and my time spent on fixing manufactures problems was less then that. So getting headers off of e-bay is a hit and miss thing. Some work perfect out of the box and others do not. So the question is knowing there will not be any more work required to get the parts to fit worth it. Other parts I have bought (replacement window regulators, tail lights and replacement soft tops) have been as good as any on the market.

I personally would not buy anything on Ebay. It is too easy for sellers to hang onto your money and refuse the return of merchandise. If you are going through the trouble of replacing pipes, I see the benefit in buying to best quality you can get, locally.

The #1 problem with eBay is quality of the product sold. Most of these aftermarket parts are manufactured in China and those factories do not have high quality control standards. You probably won't get a refund either if the parts have manufacturing defects, don't fit properly or don't function as promised. Choose your aftermarket parts from a well known manufacturer and buy them locally from a reputable retailer. You'll pay more but you're guaranteed quality for your money.