Before buying artichokes, confirm their freshness: the leaves must be well compacted, and must not tend to move or be easily depresses when squeezed with your hands. Moreover, the leaves around the stem must be fresh and not wilted. If you buy a nice case of artichokes, the advice I would give is to put them in a tub of water, just as you would with a bouquet of flowers. You’ll find that they last longer!