Two things squirrels will about kill for are black oiled sunflower seeds and black walnuts.
One suggestion I heard for squirrels was to put some black walnuts in a tub or drum of water and just wait. The squirrels will dive in for them and can’t get out.
I only feed black oil sunflower seeds in the bird feeders. As long as the squirrels keep clear, no harm, no foul, but as soon as they get around the feeders or climb the pole, fair game for the trap(s)! I put the traps right under the feeders so the ones gallivanting around the yard are in a safe zone. It never fails though, they just can’t leave the bird feeders alone.
Year before last, my whole shepherd’s hook metal feeder pole was bent over to the ground, feeders scattered/damaged. I figured maybe a bear or something had done it, but I set a bigger Hav-a-Heart trap just to see if anything turned up. Well, the culprit was a big ol’ raccoon - he actually tore some of the trap up. I was just glad it wasn’t a marauding bear. :-)