itemprop query selection

Hi,

I'm currently building a website which is a transactional tool for
businesses.  It mainly ties together two parties; companies requiring
assistance in projects and companies offering professional services.

I've done some research on past public-vocab messages and also looked into
some of the major similar-nature websites to find out how they went about
it, but have not seen anything that encompasses what I'm trying to achieve.

Currently I've segregated the site into requirements and services and am
using the itemprop JobPosting for requirements, which I'm quite happy with
and am now considering the use of either ProfessionalService or
GeneralContractor (as seen on oDesk.com) for the service section, though
this doesn't seem to allow me to classify data into things like the sector
of the business.

If anyone has any experience/ideas on how to go about structuring this type
of information I would greatly appreciate your help.

Thanks,

Sheldon