I bought some rather expensive mussels at our farmer's market fish stand, which always has a long line. I kept them in a bowl in the fridge covered with damp paper towels. When I soaked them in cool water that night, a lot of sand came out but 3/4 of the mussels were open and would not close, even when I tapped them. I ended up throwing them all out because I didnt want to give anyone food poisoning. Is it always necessary to throw out open mussels that will not close after soaking? Was I ripped off with dead mussels? I am reluctant to try again and end up discarding another 30 dollars of mussels..