Choosing A Cabling Company
There is a specific level of training and computer network knowledge that you need to do this type of cabling correctly. These are the things to look for in a cabling company: Make sure that all installers are licensed and insured, not just one person. You MUST have a low voltage, minimum in the state of CT to install any telecommunications cabling.
Make sure all installers are trained. The only way to do this is to ask for training certificates hopefully from BICSI, Ortronics, etc. Have each company that you are interested in show you their portfolio of work or references. This is important because if they are serious about what they are doing they will be more then happy to show it off, especially if they do good work.
Ask if they are BICSI members. BICSI stands for Building Industry Consultants, International and is the biggest driving force in the design and installation of code and standards based telecommunication systems. If they don't know who BICSI is proceed with caution.
Ask them if they know the ANSI/TIA/E1A 568A-5 A Commercial Building Telecommunications Cabling Standards. If so, what do they know about it.
The most common mistakes/pitfalls companies make in choosing a cabling company:
A classic move many vendors use is low balling the initial quote to get accepted over everyone else's quote then coming back to the customer once they have started the job with all the things they forgot, didn't see, didn't know they needed, etc.
PVC vs. plenum cable
If you get a quote that is half the price of all the rest you need to do some investigating. A common practice for some vendors is to quote and install PVC cable in a plenum ceiling. It's half the cost of plenum cable. I'm not going to go into the differences between a plenum and non-plenum ceiling but suffice it say that you need to get your HVAC vendor involved to make sure you get the correct answer and you adhere to the NEC (National Electrical Code).
Cable certification
Many vendors either don't test anything or use a very inexpensive continuity tester. You should have proper certification done on all your data cables and all your phone cables if you are using VOIP. Don't get fooled by someone telling you they will test your cabling. Ask them what type of device they are using. They should be using a Fluke, Microtest or HP hand held data grade cable scanner.
Not having a qualified company design their telecommunications system (creating a scope of work). If you don't do this you get each vendor's own implementation of what your network should be.
Not comparing Apples to Apples.
Assuming everyone is equal and will install a codes and standards network.