Found this thread on TriRudy and figured I would share
Anyone considering buying a new bike should definitely do some searching for used bikes because they can save a lot of money and get a bike that is nearly the same as a new model. However there are some things one needs to consider before buying used.
1. If one is shopping for a full carbon frame, be sure to check with the manufacturer on the possibility of warranty transfer. Carbon frames are expensive, can crack and buying new in this case can provide peace of mind.
2. Higher end bike shops usually provide a fitting with purchase so one should see this as a savings that can be as much as $300, but typically not lower than $100. So, buying used will mean that you need to spend the extra amount on fitting.
3. Depending on how used the bike is, it can be pretty beaten up--especially if it is being sold by a professional/semi-pro rider. These riders go through chains, cassettes, and chain rings very quickly. They also wear out tires quickly, so a careful inspection of these parts is critical.
4. Yesterday's Dura-Ace is today's Ultegra. The used bike sporting high end components may not be better (and may be inferior) to a new bike that comes with lower end components in the same company because of what is known as a trickle-down effect in the industry. The technology from high end components tends to find its way into lower end products every year that the component line changes. Probably the rule of thumb is two years max for component comparison (i.e. Shimano Ultegra today may be very similar to Dura-Ace of two years ago). Always ask the used bike seller for the series number for the component line because a new bike can be sold with older components (i.e. Ultegra 6500 is not the same as Ultegra 6700).
5. Don't underestimate the cost savings regarding taxes on a used bike. Higher end bikes come with significant tax--somewhat offset by the free bike fit--but still something to consider.
6. Most used bikes will come with pedals or you should at least negotiate this into the price because they will cost you anywhere from $150 to $300 on a new bike (which never comes with pedals).
7. Be careful when comparing USD prices to CDN prices, even when one can ship a bike from the US to Canada, there are significant shipping costs, customs and insurance can completely negate an attractive initial retail price.
8. Nobody should buy a bike without riding it first, sometimes buying used doesn't permit this because the person selling it may not be local. Too much risk involved and one should never buy used without riding it first. Buying new is less problematic in this regard because one can try the same new bike at a local shop and feel confident that their new bike from another city will feel good when it arrives.
9. Shipping costs within Canada for new bikes can be negotiated into the price most times--but it shouldn't exceed $75 anyway and this includes insurance--no customs obviously.
10. A used bike that has been treated well will almost always look brand new because riders with high end bikes like to keep them clean and looking new. Most riders take pride in a clean machine so if the used bike looks really dirty it's a good indication the bike was not taken care of.
11. One should try to make sure the used bike was kept indoors (in house not garage) during winter (this is especially important for carbon and carbon alloy frames).
12. Asking price should be about 30% less than the original asking price for the first year after purchase and then the asking price should drop slower thereafter every year. This is mostly because the components improve almost every year and (as mention above) lower end components on new bikes can be better than last year's higher end product.
These are my initial thoughts as to what I think are relevant considerations for buying used.