Ask them these questions-
Whats the actual cylinder bore diameter?
Whats the cylinder bore taper?
Whats the skirt to cyl wall clearance?
Actual diameter will tell if the engine's been bored before, or if the stock cylinder dia is within tolerance. Taper is a measure of cylinder wear, as any cylinder will wear unevenly and develop a larger diameter in the center of the cylinder and "tighter" at both ends. Skirt-to-wall tells what the actual clearance is between the worn cylinder and the worn piston.
If the taper is greater than about .007", (depends on engine family) or the skirt-to-wall greater than .0035" (depends on piston design), the engine will need to be bored and new pistons fitted. Keep in mind that if the cylinder is in tolerance now, honing could put skirt-to-wall too large. This will result in large ring end-gaps and piston slap. The result can be noise due to piston slap, or blowby and oil burning due to poor cylinder sealing. In extreme cases, piston skirt or piston ring breakage can happen. The machinist is trying to keep you from blowing the engine up and suing him.
Re-use worn pistons at your own risk.
Decking is where the cylinder decks are cut down to true them up. Performance motors are zero-decked, where the block deck is cut even with the pistons at TDC. Motor is test assembled to get a measurement, then torn down again and the block cut the measured amount. A good idea if you want to improve performance, efficentcy and reduce chances of detonation.
