2nd hand bikes - Yes or No??

Having competed at a few Tris over the last 12 months from novice to IMCH, I'm still astonished at the level of kit some people have.
I can't believe that people's first bikes are the dream machines I see when I'm racking (and usually on a bike rack leaving the event as I'm completing the run). So what I'm wondering is where the unwanted bikes go? I'd like to upgrade my bike, but would be fully prepared to buy a higher spec. bike that is maybe 2/3 years old rather than a brand new one of a lower spec. for the same price.
Obviously ebay is a source for bikes, but I was wondering if there is a 'marketplace' for used (but still in good nick) bikes?

I got my "number one" bike second hand from eBay. It had only done a couple of hundred of miles and looked virtually brand new. It was much cheaper than new roughly half price and I got it for the reserve price.

The big plus is that it's yellow.

The original owner worked in a running shop connected with a bike shop so probably got it at trade prices. He had just been accepted for MDs so needed the money.

I think I was lucky and got a good buy. However, I had to spend a bit more to replace the handle bars which were too wide and also I put a compact chain set on it with a wider rear cassette which I need for IM Nice. However, I've used the originals other than the handlebars on a time trial bike I put together so not wasted.

I also asked about a very very cheap felt bike on Gumtree that was obviously a scam when I was asked to do a bank transfer of the money. So be careful.

Like others, I also bought my bike second hand off ebay..  it was a one year old at the time and I got it for about half the price of a new one..  I met the guy and paid in cash, as I didn't want to be scammed.  Very pleased with the bike and have had no problems at all with it.   The guy even gave me the original purchase receipt and documentation, just to prove that it was his and hadn't been stolen.

If you are careful, there is certainly an opportunity to grab yourself a perfectly decent bike for less money than a new one...

Tritallk has ads for tri kit  - sometimes has bikes.
There are classified ads on the British Cycling fed website.
220 Tri magazine also has a for sale section.

Also I am selling a tri bike, been too lazy to advertise it.  If interested email me.