"Soaked" (also known as "wet" or "treated") scallops have been soaked in a bath of phosphates (or more precisely- sodium tripolyphosphate), for the purpose of adding water-weight. When scallops are exposed to a phosphate bath, they absorb it and swell - gaining water-weight, and thereby lowering the net cost to the scallop processor. (Keep in mind, that when you buy "soaked" scallops - you are paying for this added water.) The absorbed water evaporates when the scallops are cooked- leaving them smaller, tougher and less-flavorful than their dry counterparts. It is generally easy to discern treated scallops as they will usually appear very white in color.
"Dry" is the seafood industry term for natural scallops, which have not been treated with phosphates. Natural scallops have a slightly tan, or "vanilla"-color. Dry scallops are superior for the following reasons:
For searing purposes, dry scallops caramelize beautifully!
Dry scallops taste sweet & natural, where "wet" scallops can sometimes have a washed-out, or even slightly "soapy" or bitter flavor.
You are not paying for added water with dry scallops.
"Soaked" scallops are very common.
FYI - A quick search shows Sam's sells both. There is no regulation that requires that be made clear on the packaging, so be wary. Look for the type that clearly says no chemicals/water added.
You can find high-quality dry scallops - but you will need to go to a reputable seafood dealer, and ask.