Installer/sales rep responsibilities

["JW" <golf4nospam@xxxxxxxxxxx>]

We're a small company.  Our installers and sales reps act as a team to
complete
projects they do together.  Sometimes they are able to spend time going over
a
job before the final proposal (usually larger jobs); other times, the
installer only
sees the project after the sale.  The sales person designs the job and puts
together
a rough parts list and it's reviewed by the installer before ordering (by an
in-house
 technician). For a variety of reasons, the original parts too often require
a change.
Too often, this requires phone calls and research to find the right part and
review the
specs, codes, etc.  Our installers also serve as limited project managers,
co-ordinating
schedules, sub-contractors, etc.  Who do you have finalize the parts list -
the person
who designs/sells or the technician who installs it?  Since site time is
valuable, there's
concern with the office/phone/computer time required to research/engineer
the final
parts list/design.  Any insights on how things are handled at different
companies
would be appreciated.

Thanks!