A fusible link will not (should not) be found in the ground wire.
They are only used in the positive wires which is adequate to protect, in addition to the fuses, the vehicle circuits.
Any "real mechanic" will know this as just about every car built since (guessing) the 70's till the 90"s will have them. Then later, as more and more accessories were added fuses were employed which provides better protection of the vehicle wiring.
For piece of mind you may want to look for a new mechanic.