Whether you homeschool or are enrolled in your local public school, your children have a right to any gifted or special education evaluation resources that other residents of your town have. Whether they test for gifted is another matter, having mostly to do with funding (or lack thereof) for Javits.
You can get substantial variance between overall experienced and inexperienced testers, mainly having to do with knowing when to query ambiguous responses, and in maintaining an appropriate and engaging pace. Also, some newbies have not yet mastered neutral responses to children, that don't telegraph the strength or weakness of the performance. Depending on the child, these tells may discourage or encourage them...or merely be distracting.
The difference between experienced testers in terms of their specific experience with gifted children mainly affects engagement, pace, and interpreting low-frequency responses. Gifted kids often come up with responses that are correct, if you think about it differently, but are not in the manual. An examiner unfamiliar with divergent thinkers may score it exactly according to the manual, and just move on, rather than probing to see what the reasoning is, and how it might actually be a higher-level correct response. Many gifted children are more perceptive about the examiner's own level of engagement, skill, confidence, or intelligence, which can affect their willingness to produce optimal performance for the examiner. In rare cases, you may encounter an examiner who is vaguely resentful, or insecure, about testing a child who may be markedly more cognitively-able than themselves. Obviously, that would have implications for the validity and accuracy of your results.
The pre-publication purchase price for the WISC-V is good until October 18th, so I would imagine they are planning to start shipping around then.
