I do far more home visits than estimates over the phone.
I know this might fly in the face of a lot of what you may have been told but I find that I can obtain additional work if I actualy visit the home and speak face to face.
When asked to price for carpet cleaning Iwill also make a note of other flooring areas ie hard floor,Amtico etc and when I send them the estimate for carpet cleaning I also price for these areas seperately.They have the option to take you up on it or not but if asked why I have done this I just say it's for future reference.
It's amazing the amount of people who will decide to have this work done.
Its the same for upholstery, rugs, stain proofing etc there is always something you can add to the estimate as an 'optional extra 'with out the hard sell.
Simple and it works.