Need to clean air ducts?

[Greg Smith]

We have a newer tenant that has seemed to be very good so far. However, he has been complaining of his allergies acting up since moving in and is asking for us to clean the air ducts thinking it is due to dust in the vents.  He has gotten the carpets cleaned and we have already tried replacing the filters. It's a small house but having someone clean the ducts would cost a few hundred dollars at least. Has anyone done this in their own properties?  Would you expect the tenant to at least split the cost? Thanks