Table quality garlic can be as perfect as seed quality, but it is not required. Table garlic is smaller (sometimes quite small), can be found with damaged wrappers, sometimes a soft clove or two, and may have disease that does not affect its edibility. If you grow table garlic, your concerns are yield, so you will toss the obviously sick, and sell the rest. If you are a seed grower, one diseased bulb (white rot, bloat nematode) can terminate a field's seed.
The garlic on the left is high-quality seed stock garlic purchased from Oregon, the garlic on the right is high-quality table garlic purchased at NYC Greenmarket. If you feel tempted to plant that farmers' market garlic (it is big and beautiful after all), don't. Several of the diseases in NYS fields will remain for years once they are introduced, and many can be hosted by any allium species in your garden.
When you buy from a farmer touting seed garlic, you enter a trust with him or her that they're honest about the health of their fields. They cannot know everything, and healthy looking garlic can harbor disease, but that farmer should be observant and resist selling anything as seed that has come from a field showing signs of the worst diseases. New seed in the field will be quarantined until it reproduces year after year with no disease. Old seed is trusted seed and a seed grower will be wary to ever run down his or her supply.
These are two seed stock quality bulbs from Washington state. Porcelain 'Georgian Crystal' on the left and Rocambole 'German Red' on the right. At 3.5 plus inches, it is arguable that these are too big. Giant bulbs have less flavor and may be more difficult to cure successfully for long storage, but no matter, you won't eat these -you'll plant them.
The best seed bulbs run from 2 to 3 inches across. Farmers' observation has long proven that the smallest bulbs and small cloves will produce weaker plants. They will grow, but less vigorously, and you will find small cloves on small bulbs at harvest time. Last autumn I planted garlic seed of the same cultivar from two different sources. One delivered medium-sized bulbs with medium-sized cloves. Another delivered giant bulbs with large cloves (the one you see above left). Both were sold as seed.
The soil and cultural conditions were consistent row to row. Yet, this image shows the difference between the two. The garlic on the left is nearly twice as large as the garlic on the right. The plants look healthier too, a deeper green with thick-stalked scapes. They are the very same cultivar grown in the very same soil -the only difference was bulb and clove size.