Hardwood mulch can be a host of various forms of fungi. You have to understand that hardwood mulch is breaking down constantly, thus micro organisms are present as well as insects. That is just the process of mother nature. There is a problem in my area of what we refer to "Dog-Vomit" fungus. It appears as just that, as if you or your dog upchucked on the mulch. Once this dries, then the spores are air born. What we do is just take a shovel and flip it over to hide the not so asthetically appealing site of the fungus. There is another one that I can't think of the exact name, but I will refer to it as the "Shotgun" fungus. This is probably what the car salesman is most likely refering to. This creates spores that can actually rotate to light. So in your case, a nice shiney car that is reflecting the sunlight is a definate attractant. It then shoots out spores that can go as far as 14 feet. It is really noticable on siding and anything with a light color. I even had it at my previous residence. These spores are not easy to get off. The local extension agent for my area just recently spoke on this at a seminar, and said that even pressure washing is sometimes not effective in removing the spores. I like the idea of pinestraw, though in your area it might not be readily available. I would suggest advising him on making a capital expense improvement and look into installing stone or switching to bark mulch. Bark mulch does not break down that fast and is very light. Check with a local University and their plant and soil science dept. or contact your local extension service for some other ideas for your region.