Actually, SellerKey is very good but any of their 'free members' who just signed up to be a seller are going to be bad.
I would avoid anyone who just signed up like the plague. If possible, start a conversation with them and talk to George or someone there.
They are very responsive and helpful all the time regarding orders. They are MUCH more reliable then certain places, though they aren't completely better than DHGate....they just have less counterfeits or issues to deal with.
SellerKey is overall a good place to trade if you can start a conversation, and get a brand name product. The manufacturer will be listed for instance: Canon. The others you should avoid.
And really SellerKey is very easy to use and has all its own reviews written about it so check Salehoo's official reviews. Its a good bet.
But its NOT scam free, so don't deal with anyone you aren't sure about.