I was recently contacted by a customer who had a suggestion that I can't believe never occurred to me because it's so simple. If you sell wire hook style earrings include those little rubber stoppers so they can be worn more securely.
These are also useful if you display your earrings on hang cards at shows they they won't fall off the cards when people handle them.
These are really easy to find, most jewelry supply stores carry them as do most department store jewelry sections (but in smaller quantities and they cost more). You'll usually pay between $2-$5 for 100, even less if you buy in bulk.