If you're new and don't know anything, buying local or not doesn't help. It helps to an extent that it works on the spot, but the next time you use it .. it could be busted :\
Trader rating does go a long way, but doesn't mean that the product won't be "broken." I've done numerous of trades, some bad, some good.
As Hectic stated, if it's a cheap brand like G&G lower end models, CYMA, JG, etc.. just buy them new.
Only when you start going 300+ I'd look into used VFC's.