I buy from there with regularity – looking for bargains on stuff I’ve previously considered buying, or have purchased at regular price, or looking to explore stuff new-to-me – and have never found it to be a dumping ground for flawed/damaged wines. I reckon you’ve just had very bad luck. FWIW, K&L will take back flawed/corked bottles no questions asked; I’ve taken them up on this standing offer on more than one occasion.
Second the K&L idea…I would add Kermit Lynch for good value with consistency. The range cited (9-15 bucks) is a bit of a tough one to reliably nail. I would avoid Bevmo (both the Wilfred Wong hype thing and questionable storage), as well as Costco unless you’re buying specific bottles on reliable info. Also, I agree that the cheapo 90+ pointers at Costco are invariably Sierra Carche-type stuff.