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You can use Pathfinding behavior to move customers to a random point in the supermarket, or to a random shelf. When arrived to the shelf, perform some animation, then choose the next random point. After some time, use Pathfinding to walk to the checkout.
One problem though - Pathfinding will not work correctly on isometric grid. Try searching this forum for possible solutions. One solution that comes to mind is to use a separate (invisible) 2D grid or tilemap for Pathfinding.