Hello there this is Ed from Mooduscycle and I thought I'd share a few tips for happily buying used motorcycle parts. There's a lot more to it that you may think, so here we go!

1. Know what part you really need. This may seem simple but just because your bike won't crank over and has a new battery doesn't mean the starter is bad. Get a service manual and test; don't guess. It gets expensive and time consuming, never mind frustrating, buying and replacing parts that weren't the problem in the first place. Get a service manual or ask someone for help to determine what you need.
2. Know your motorcycle. A CB750c is different from a CB750sc in a big way, but some sellers don't differentiate and simply put down CB750 when listing the parts. If the seller can't verify exactly what bike the part came off then matching part #'s is the best bet, but looking at the picture and matching up connectors will also work just fine in most cases.
3. Find out what will interchange. This tip takes some work on your part but can save you a lot of money. For instance if the petcock for your bike is hard to find or very expensive, you can find another more common one that will work just fine even if it looks a little bit different. Specialized users groups and Google are good for obtaining this information.
4. Call your dealer and see how much the part costs new. You may be surprized to find out that headlight switch for your 1998 VFR can be had for $27.00 brand new at the Honda parts counter. Alternatively the voltage regulator is about $400 and can be had used for $50 or so on Ebay.
5. Buy spares before you need them. I may be biased because I sell parts but I would rather have a set of igniters I paid $80 for in my toolkit than have one go bad on the road and have to pay for a U-haul truck to get home because they are obsolete and unavailable. Spares I think everyone should carry on a bike that is more than 10 years old: Voltage regulator, igniters, lighting relay, fuses, headlight bulb. These are parts that go bad and leave you stuck, they are also easy to swap out on the road. Carrying a spare piston may not be such a good idea.
6. Get to know your seller. Gruff folks that sell things !!!AS-IS NO REFUNDS! CASH ONLY~!!!111 scare me. Why not keep looking and buy from someone that will issue a refund if there is a problem? Why wouldn't someone want to take Paypal? Look at the feedback ratings. Every seller gets a negative now and then but take a look at what the item was and how it was handled. Comments like "fast shipping" "Better than I expected" are usually a good sign that you will get your stuff fast too.
7. Ride safe. In my part of the country now is the time for modifications, restorations, and snowmobiling as the roads are all sand, salt, and ice, so stay warm and if you are lucky and have clear roads pin the throttle on my behalf. Thanks for looking at my guide and I hope it was a little bit helpful.