Just wondering if any one had experiences working with third party vendors to develop a customized skin.  If so, what are some of the issues you ran into and any advice in selecting the developer is appreciated.  Thanks.

Client references are always helpful also, as well as examples of other work.  Developing a skin is both an artistic and technical endeavor and it makes sense to ensure that you like the type of work your "artist" tends to produce.  Also, be sure to properly set expectations between you about cost and effort.  As previously mentioned, you should expect to go back and forth on some tweaking but too much tweaking can make the work unprofitable for a designer.  Its in your best interest to pay a reasonable price so that your designer is engaged and welcomes your feedback.

The advice given below is also excellent.

Scott Willhite, Co-Founder DNN