Buying paraglider gear on the second hand market isn't quite as risky as buying the canopy itself. Until now, I have basically been talking about the canopy and lines of used paragliders. But of course you need some other paraglider equipment to actually go flying on a regular basis.
Let's assume you are starting from scratch, and need all the basics.
It's worth getting a great harness, even if you are flying older used canopies for a while. With proper care, this piece of paraglider gear will last you the entire length of your flying life. Hence, in the long run, getting a cheap harness which you end up replacing will just cost you extra money.
Also, for safety's sake, it's a good idea to get the latest back protection from day 1.
If you intend doing high flights, you will need a reserve 'chute. By 'high' I mean high enough to have time to deploy the reserve! Not much good while slope soaring, but a must for most thermalling flights. Like harnesses, a decent reserve chute which is cared for and packed properly will last practically the whole time you are flying.
But be aware that used reserve parachutes might have issues. It's worth doing a bit of research to track down some manufacturer's info. While researching this, I came across a guy relating how he used his second hand reserve chute for 2 seasons of flying before discovering it had a flaw which had been detailed by the manufacturer. Oops. The guy himself used a slightly stronger term than Oops...
Ankle-protecting boots are a good investment, and a very wise purchase for a sport where you hope to land like a bird most of the time, but occasionally don't...
Glasses or goggles should of course offer 100% UV protection for your eyes. And at 2000 meters (6000 feet) nobody is going to notice how trendy they are. Just my personal opinion, maybe you disagree. :-)
Helmets should not restrict your vision too much. Even if they are full-face in style, they should be designed to let you to hear the air slipping past your head. So a model that fully covers your ears is not a good idea for flying.
Most pilots who buy used paraglider gear also purchase a two-way radio and a variometer. You can buy these second-hand for half the cost of new gear, but just keep in mind that they won't necessarily keep working as long.