When choosing a vendor, what are some things IT staff should keep in mind?
We've found a few things: longevity, how long the vendor has been in business doing this type of work, their depth of experience, the skill set, and how they portray their best practices to us. What we also keep in mind is how they understand our infrastructure.
I think they should be able to acknowledge and respect your requirements, while as a client you appreciate their input and recommendation.
What about establishing a good relationship with vendors?
A good tip is to make sure that your contract is established properly, and make sure you establish a good working relationship with the vendor's project manager. Another tip I would recommend is to be willing to give and take. Let vendors see that you're not trying to nickel-and-dime them. I think vendors respect a client who is willing to be flexible when it comes to the workload, cost, time, and so on.
What if a relationship turns sour?
When that happens, I think you meet with the project manager or someone above the project manager and acknowledge that you're not happy. Acknowledge that their work product has changed, that their services are no longer meeting your needs. Be honest and give feedback. Be very clear as to why you're disappointed. Herein lies the reason why it's good to have a good termination clause in your contract—make sure you have a contract that protects you against them in the future.