For used records try discogs.com. I've received some NM in very good quality, some average. Always assume the seller is exaggerating about the condition, look for mint and near mint. Always message seller before a sale to confirm the record is the version you want.
Discogs is a great tool as well. It is a database listing every release, country of origin, etc.
I've bought used from Academy Records online (a NYC store). Good quality, return policy, but not cheap.