Hi Sparky78,
Sure, there's lots of stuff you should avoid. In the words of Elmer Fudd; "Be Vewy, Vewy careful".
It depends upon how old the gear is. You need to know your stuff if you are buying 2006 or older. Most gear from 2007 was pretty reasonable, with a few exceptions, wink wink. Dont buy hi performance gear to learn on, you'll just trash it and it will slow down your progression and possibly injure you.
Buying from most of the big 7 can't go too far wrong. Airush, Naish, Cabrinha, Slingshot, North, Flexifoil and Best. Plenty of others out there made good kites too but their resale isn't what it could be and their durability may be questionable.
If you have any mates in the sport, ask for their guidance, asking anyone who sells gear will just confuse you as their strong bias towards their own gear clouds their ability to see good in other brands.
Good luck with it and welcome to the sport,