What's the common faults ( if any) to look out for on a superfour?

I know on some model the exhaust is mild steel so potentially could rust but is there anything else?

Sometimes the gear shifting seems to be sluggish.. I'm not sure if it's only mine. But I heard many cb400 has that issue.

i am not claiming any expertise but i would consider the following when considering a bike such as the superfour:

these are learner and novice friendly bikes. it's unfair to tarnish types with the same brush but often these owners / riders are younger and have a bit less money so maintenance is often neglected. novice riders tend to fall off or drop bikes too, so check for accident damage. frames seem to survive fairly well but clocks, lights, fuel tanks and engine cases are often scarred.

some honda parts prices are scary - hence check rear shocks, exhaust and other easily damaged and corroded parts for originality and rust. cheap chinese copies are available and common. (and cheap for a reason.)

also these bikes are at their awkward age - old enough that values have bottomed out so nobody (apart from me perhaps) is renovating / restoring them (yet?). this means they are cheap to buy but not worth spending money on. with this in mind condition is everything. it's worth spending a bit more for a good one rather than buying a cheapie and doing it up.

so in summary, common faults are:
accident damage
poor maintenance / little to no history
rear shocks, clocks, front light and exhausts worn / replaced cheaply

other than that check everything as you would for any other bike - tyres, bearings, chain and sprockets, fork seals, brake fluid and pads etc. should all be in good order for any bike that's to be used on the road.

cheers bludclot