Boil potatoes in skins for 20 minutes. Drain and cool, then dice potatoes. In large bowl, toss potatoes with olive oil and garlic and then cool to room temperature. Add feta and scallions to the potatoes. Drizzle with vinegar. Add dill, salt and pepper. Toss gently. Allow the salad to sit for 1 hour. Garnish with olives and serve.