Having thought about this for a bit,
1) Test administrator criteria may be found online, here is one source of
Examiner Qualifications.
Reading this, I would understand the test administrator to be qualified credible, legit, etc.
The questions which remain (and where I would focus my continued research) would be on exploring how well the test results and score report would be a "fit" for planned uses. I most often suggest looking at the "primary source" for information. This is because information can change rapidly and without notice, and it is important to have confidence in what informed our decisions.
2) You may wish to know whether the test you are looking at may be different than the tests accepted by DYS. My thought,
WJIII Achievement math/reading only may not be a match with
WJIII Cognitive Battery. This is something you may wish to explore.
3) Reading "Offers Individual PIAT or Woodcock-Johnson testing which can be used to meet the 3rd, 5th, or 8th grade testing requirement", I would understand this to be a
limitation of the test results and score report to these stated purposes. This is something you may wish to explore.
If the answer to #2 is
a match, and the answer to #3 is
no limitation, you may wish to work with this tester and enjoy the savings.
Other answers may indicate this would be a useless test
for your purposes. (Not a useless test, not a useless test administrator, just not the right "fit"
for your purposes.)
Other posters may have other questions to consider to help inform a decision, or other methodology for making a decision.