Some people have already pointed out that a proper Kakuro has exactly one solution, and that said solution should be reachable by deduction, no guessing or backtracking needed.

Furthermore, I frequently encounter Kakuros with an additional constraint: no permutation appears twice in a puzzle. That is, if the puzzle has two clues '5', one must be 1 + 4 (or 4 + 1), the other 3 + 2 (or 2 + 3). But this constraint certainly isn't universal.