Why risk it you ask? I can give you a couple examples when used gear is the way to go.
1) If you are a newbie, just getting into balling, and you go out and drop a pile of cash on just any gun, you may very well get out to the paint ball field and find you like certain things about a Tippmann vs. a Spyder.
2) Multiply that by a family of four and this hobby can get spendy fast.
3) Cutting back on the price of equipment leaves more money for throwing paint. Just saying.
So what do you look for when you are finding those sceaming deals?
Markers/Guns, consider the asking price vs. the risk. If the asking price is 50% off a gun that doesn't work, often times a repair kit and Youtube video are your friends. There might be some extra wear and tear on the outside, people do crawl through the mud with these things in tow. Saving a hundred bucks maybe worth a battle scar or two. Just make sure you are investing in a good gun. This is where your research is critical. You don't want to spend a fortune repairing a dimestore POS that never shot right in the first place. But, you get a high end marker for half price that just needs an O-ring replaced. Score!
"99% of issues with a marker can be tracked down to either 1. lubing the o-rings / replacing them 2. make sure the battery you are using is a new Duracell or Energizer 3. the macro line is loose, either cut the tip off of it with a razor blade and reinsert or add a drop of BLUE lock tight to seal the leak."-Ebay (Rush Products)
Masks are often a good find, especially if you come across a high end mask someone is getting rid of because the lens is scratched. By design, it is fairly easy to replace a lens since they get scratched so easily.
Hoppers and loaders, meh. (shrugging). They could have cracked plastic and not work properly. They are usually a pretty cheap item to pick up new. I wouldn't bother. Unless it's free. Free is always worth the risk.
Tanks are tricky. They are a great deal if they work. It's hard to see any problems until you use it. But they are a spendy item so if you get a good deal, might be worth it. This is where it is important to ask the seller questions.
Harness's / Pod Packs are a great find if the price is right. Watch for hidden rips and streched out elastic.
Pants and Jerseys are expensive. Esp with built in padding. If you can find these, grab them. Negoitate on the price. Who cares if they are stained or out of date? The padding makes it all worth while. :)
Gear bags are a spendy item when purchased new, so if you find a good deal on one, don't be shy of a little tear or dirt. Some fishing line is sturdy enough to repair a gear bag. And cleaning a bag isn't a difficult task. A good deal is worth the elbow grease.
Barrels, oh yeah! Grab them. Not much can be wrong with those that isn't cosmetic. If you don't mind a scratch or ding, you are going to save picking these up used.
In my research/experience the only thing I've seen be a hard no on buying used is CO2 tanks and barrel swabs. Too much can go wrong and they are cheap purchases to begin with, so the savings will not be worth the risk.
I hope this gives you some ideas on what to look for when considering buying used gear. See you out there!