Sometimes, during a consultation, a client will review work with you that they are looking to have done that falls outside your scope of work, and a subcontractor needs to be brought in. It is so important that the subcontractors you choose are people of integrity and will work just as hard as you for the client. You should not only have the same business ethic, but similar practices as well.
The client tends to get used to how you work, how you bill, and your level of customer service, so it is critical that the people you sub in provide them with the same levels of service that you do. They are tied to your name after all. If the client is unhappy with them, they are inevitably unhappy with you.
Different people work better or worse with certain personalities, so you want to make sure that your subcontractors are similar to you in personality as well.
I am currently working on a job where I contracted in my IT team to do network and computer system integration. The IT team I work with is a group of brilliant guys who know their stuff and are always available for over-the-phone tech support. My client has been working directly with them for a few months now. I recently found out, however, that my client has been completely frustrated because he had an issue with his system, and while trying to troubleshoot over the phone, he could not understand the technician at all. On top of that, the team came out a number of times to address the issue to no avail and sent him a large bill for the numerous trips without letting him know that there was even a charge.
As smart as my IT team is, they just cannot seem to communicate clearly with this one particular client. Now, I have to resolve the issue for my client because this whole situation reflects back on me, even though my portion has been executed without a hitch.
Subcontractors can be essential to the success of your custom integration company, if hired properly. They can add an expertise that your company may be lacking or fill in other staffing gaps you may have. If you hire them properly and train them in your company culture, then the results can be spectacular for you and your client. If not, the whole process can make you question the idea of ever hiring a subcontractor again.