3 star potential is star-allstar I believe. Depends completely on your scouting situation wether you can find perrenial allstar or better (AKA 4-5 star potential), I'm sure there are few but they become harder to find with 4 unscouted or below. If you have 4 star rated scouted players who's potential still unknown, your best thing to do is scout them as doing the unscouted will cost extra and will have slimmer chances anyways.