When you pop the cork, if its a ruined bottle, it will often look kind of slimy and have some green tinge to it; sort of mouldy looking.
When you pour the wine and smell it, it'll have a wet newspaper smell to it.
Next if you get to the tasting part of it, sometimes in a white wine, it will have a slight effervescence to it and if it is a still wine it should not have any fizzy characters so the wine is probably bad.
It always sucks to get a bad bottle of wine. Especially when you only picked up one bottle, and you were really looking forward to it. You get home hoping to relax with a nice glass of wine, or to enjoy it with your dinner and then you get a big whiff of something nasty in your glass. Don't worry though, its not as rare as you'd think. Supposedly 1 in 10 bottles of wine is ruined by cork taint. So if you get a wine that you've had before and you thought you liked but its bad this time. Don't worry you can always take it back and exchange it for a new one, or something else because chances are, its corked.
The liquor or wine stores should never challenge you on this. If you say its corked, its corked and they should give you your money back. If they don't, ask to speak to a manager.