Grilling Oysters

In "How to Grill", the recipe for grilling oysters says to test for freshness by tapping them on the work surface to make sure they close their shells and to discard any that don't.

I recently purchased 6 oysters from my local supermarket which appeared to be closed when I got them. I stored them in the refrigerator for several hours before removing them for grilling. All appeared to be closed when I removed them from the refrigerator. I grilled them as indicated, but after 10 minutes, only one had opened. I did manually open another one, which smelled and looked OK, but was reluctant to eat it. I ended up throwing away 5 of the 6 I purchased and was extremely disappointed.

Any other tips on knowing if purchased oysters are fresh if they appear to be closed from purchase through the start of grilling? I hate to purchase twice as many as I need just to make sure that I get enough of them to open on the grill. Should I trust the supermarket counter person if they tell me the oysters are fresh?

Thanks for any advice you can provide.

When storing oysters, or any mollusk for that matter, in the refrigerator you have to make sure thery get air to breathe. I know that sounds silly but its true. When the kid behind the counter at the store ties the plastic bag in a knot he thinks he doing you a favor by saving you a mess but what he's really doing is killing your dinner. Oysters are actually pretty hearty little critters, I know guys who literally bury a bushel in the ground and simply dig them up and eat them year round. This only works as long as they don't freeze though. So next time you buy your shuckers try transfering them to a container with a damp paper towel or if you have a larger quantity try a brown paper bag with a little moisture added. This should help keep the little guys kicking until you're ready to do 'em in on your time.
Good Luck and Enjoy!