Some clues to tell if the wet sand has been "going out" : Firm/hard to the step (can't leave a foot-print per se). Waves are glassy blue (versus brown/dark d/t suspending sand). Aluminum and light foil and stuff (or just plain sterile). If the wet sand is not producing, then that could mean that sand is generally coming "in" at this time (sans targets). In which case, you'd be relegated to the dry sand. And the obvious would apply: Wherever people frolick the most But if you're in a heavily hunted-competitive area (lots of other md'rs), then sometimes you'd need to be creative and avoid the *obvious* spots (volley-ball courts, etc...) and go to where locals may not harvest as often. Eg.: towel line "further down", etc.... If the towel line all over is sterile, then it could mean that this high-water area you're hunting is new (ie.: less than a year old) built up after past surf events. In which case try further back towards the cliffs or dunes to see if that makes a difference.
