Hey Giles,
There are plenty of topics about buying 2nd hand on this site, use google for a quick search. I also think Laurie has posted some guides to buying 2nd hand in the the news/articles on the home page;
www.seabreeze.com.au/Articles/Kitesurfing/Summary.aspxFew basic things to look for/ask when buying 2nd hand;
- If possible its better to see the kite in person (rather than buy online - tho reputable shops might be alright if you know what you're after)
- Any repairs to the kite (and who fixed them)
- Wear on bridles/lines/pullies
- Bar (make sure they aren't damaged, worn)
- Safety/quick release works
Hope this helps!