Marcus catching cropped knob-and-tube on a 1928 two-flat is exactly the thing you are paying for. Balloon framing and vintage electrical are two of the nastier surprises in that building stock, and an inspector who works that era regularly has a mental model that a generalist does not.
The part worth naming: the $475 fee is not where the value calculation lives. The relevant number is what the K&T remediation quote would have looked like, plus the insurance conversation that follows, since a lot of carriers in Illinois either exclude active K&T or price it significantly higher. You would want to confirm current insurer positions directly with a broker, but that cost exposure tends to dwarf the inspection fee by a wide margin.
One thing you did not mention is whether Marcus also flags deferred maintenance on the common systems, things like the boiler, the sewer lateral, and the roof drainage that a two-flat shared between units tends to accumulate. On a 1928 building near Humboldt that is where the next expensive surprise usually sits. If he does ongoing maintenance inspections rather than just purchase inspections, that is worth knowing before you close on a deal rather than after.
Pass along the contact if people ask. A credible inspector who knows Chicago vintage two-flats and does not soften findings to protect agent relationships is a useful person to have in a network.
What was the listing price, and did the K&T finding give you room to renegotiate or did you walk?
