- check NADA and Kelly Blue Book first - before you even ask us. NADA gives a low and average retail price; KBB gives a single retail price that is usually higher than the average NADA price. In all cases, these are meant to be prices from dealers... on a private sale, you should expect to get somewhere between the two NADA prices for a bike in average condition, or ~10-20% below the KBB price.
It may sound obvious, but condition is a huge factor. The NADA and KBB prices are for average to slightly-above-average condition; you can ask a premium for a bike in totally mint condition without a single scratch or flaw.
On the same theme, expect less - a lot less - for a badly scratched-up bike, rashed on both sides, with a cracked front fairing, a dented tank, and scuffed engine covers. New side panels cost ~$300 each, new front ~$195, seat sides ~$125 each, tank ~$400, peanut and generator covers ~$50 each (prices from Flatout, including shipping).
Mileage is important, but less so than condition. KBB even has a table estimating what they think "average" mileage is for motorcycles. In my opinion, a YZF600R three years old or newer with 15,000 miles or less is "low mileage". Buyers may run away from a bike with more than 30,000 miles, but in most cases (at least with the YZF600R) they shouldn't. Our members have plenty of experience with much higher mileage than that and no major engine repairs. If you're selling a high-mileage bike, you may have to wait a bit longer for a knowledgeable buyer, or else accept 10% less.
If you've kept a detailed maintenance log, it adds to the value, especially to a knowledgeable buyer.
Take into consideration the "wear items": tires, brake pads, chain and sprockets. If you've ridden your bike for a while, you know how expensive these items are. If you're selling an otherwise perfect bike with two bald tires, expect $250 less for it.
Keep the cost of a new YZF600R in mind. For example, as of right now (1/7/07), many dealers are selling new 2006 "leftovers" for $6,100. In light of that, it might be hard to find a buyer who will pay $5,500 for your 2004 with only 6,000 miles but that needs a new rear tire and wil need a new front soon.
Mods, no matter how much you love yours and how expensive they were, seldom add much to the resale value. Inexpensive, popular mods - flushmounts, for example - are usually a wash: they don't affect the price enough to try to sell them separately. Very expensive pipes, racing suspensions, etc. are sometimes worth more if sold separately.
Custom paint jobs, no matter how nice, often lower the resale value. To get your money's worth out of that expensive custom paint job, you will need to wait for the buyer who loves it as much as you do.
Mechanical problems, though rare on the YZF600R, kill the resale value. The most common problem - bad second gear - is somewhere around a $1,000+ fix at a dealer. If you're the proud owner of a YZF600R with a dead second gear, try steering potential buyers here first to learn about how to deal with the problem. It's a 1 to 2-day fix for somebody with reasonable mechanical ability, and costs about $250 in parts. If a buyer knows that he can fix it himself, he might be a little more willing to buy it.
Meanwhile, fellow 'Cat owners...please add any advice I've forgotten. I tried to remember as many points people have made over the years as I could.