You should only flip salmon one time. After about 4 to 6 minutes, the salmon should release easily from the grill grates. If it’s sticking to the grill grates, it needs another minute or so before it can be flipped.  If you repeatedly flip the salmon as it’s grilling, it will cook unevenly and the edges will never caramelize properly. Those golden edges are the best part, so resist the temptation to keep flipping your salmon filets.