Through-hulls and seacocks are metal holes in the hull, usually bronze. Whether they should be wired together, bonded, to the anodes and the boat's DC negative is one of the longest arguments in boat electrics. A surveyor's job is to see what's fitted, whether it's coherent and whether the fittings are corroding.
The two views
Don Casey, answering in SAIL, says underwater metal that is or can be electrically isolated should not be bonded, and notes bonding has the opposite effect for stray currents in the water, inviting damage. He also notes the ABYC standard recommends tying all underwater metals together for corrosion control.
Nigel Calder, in Good Old Boat, says in general no for bronze in wood or fibreglass hulls, because bonding speeds up zinc consumption and generates alkaline hydroxides. His exception: if a fitting could be part of a stray current path, bond it, because zincs can't stop stray current.
Either system can work. A half-bonded system, with some fittings wired and others not, and corroded wires, usually doesn't.
How a surveyor checks it
Follow the green wires from the bonding strip to each fitting. Check every connection for corrosion and tightness. Look at each through-hull and seacock: pink, pitted bronze means the zinc has gone out of the alloy. Note which fittings are bonded and which aren't, and whether the boat lives on shore power.
What decides the grade
The fittings. Badly corroded or pink fittings are an A, because they can fail. A broken or inconsistent bonding system is a B. A coherent system with good fittings is a C to record.