Your confidentiality is extremely important. I know what it takes to win customers, create business processes, and grow a team of qualified linguists -- that's why I not only insist on signing your non-disclosure agreement, but I also have my own to make sure you're protected.
Customers
I do not share customer information between my clients. If a project or assignment requires contacting your customer, I do this on your behalf (frequently clients create an email address for me). I never contact your customers once a project or assignment is completed.
Vendors
I do not share vendor information between clients, nor do I offer vendor recruitment as a service. I'm willing to interact directly with your vendors, but do so only upon your request, and don't contact them after project/assignment completion. That said, it's inevitable that I may have already worked with some of your vendors with other clients or directly. If you ask me to work with a vendor I use myself, I discloses this immediately to avoid conflict. The localization industry is a tight-knit community, and the last thing I want is to have my clients worry about confidentiality.