You would have to test his/her sample with a validity test strip to see that the creatinine and specific gravity are within satisfactory limits. These are essentially the same colorimetric tests that are used at the lab when they run the validity tests on the sample (which had become SOP in recent years, making sample "color" the least aspect in determining an overdiluted sample).
These kits are inexpensive and are found online by doing a Google search for "drug adulteration test kits"

Without the validity tests, you would have to chance it by taking his/her word that s/he had not consumed an abundant amount of fluids prior to donating the urine sample to you (iffy, iffy).

Do you have access to a sample from a different clean person?
Burnt Toast Reviewed by Burnt Toast on . Gc ms testing ( drug test soon) advice? Hey how's it going? Started doing some gc/ms testing on myself at a local lab, to see how my body metabolized thc.. So anyways 3 weeks into being clean I tested at a quantitative value of 71 ng/ml and week 4 for I tested at 47 ng/ml.. Both tests were around the same time of the day (9am). I'm having trouble understanding the value of this test..I'll be around 40 days clean at the time of the drug test.. I have a drug test next Friday for a pre-employment at a local hospital and I'm just Rating: 5