bottom line....this doenst sound like a fuel problem. sounds more like normal maintenance or sensor problem or a elctrical problme but we need to find out more about what the car is doing.

if his car was running rich...it would show on the back of the car. regardless if his tailpipe is sooty or not. it would show. hondas dont run lean from the factory. they have a better fuel injector design and also employ a better engine control management that reduces emissions sooner and uses the latest improved catalytic converter technology. there is also technology in having the car warm up wuicker which makes the cat. work better. a vapor locked gas tank improves fuel not getting into the atmosphere. having the cat closer to the engine also helps warm up the cat. these are just some of the things that honda does to make thier cars run more effectivly.
as for your last sentence??? quit trying to save face. maybe you should ask "is your car overly modified in any way?" but you didnt ask that...you asked to check his tailpipe. and once again...you say he should be throwing a code. i have had many of times witnessed and fell victim to hondas running crappy from sensors that have never once thrown a code. this is from 02 sensors to map sensors all going bad without the cel going off. the cel is somewhat a diagnostics tool but the ecu does miss things here and there.

to end this whole thing....we need to find out more about what the car is doing