Unless you ACTUALLY have mold or ACTUALLY have vermin living in the ducts or ACTUALLY have duct blockage, a case can be made to not spend your money on duct cleaning per the EPA.

http://epa.gov/iaq/pubs/airduct.html

Generally, never.

true.
if the system is well sealed there is no need
for duct cleaning.

when they cut the holes in the ducts..did they
screw them shut and mastic seal them?
I've seen systems where duct cleaning holes
were improperly sealed.

keep in mind that they are selling you a service.

best of luck.

"when they cut the holes in the ducts..did they
screw them shut and mastic seal them?
I've seen systems where duct cleaning holes
were improperly sealed. "

Anyone that cuts holes should close them up adequately and correctly.

Why do you think there is material in the ducts that needs to be removed?