don't trust a test you buy at CVS.
And why shouldnt they trust a THC test kit from CVS (or any other pharmacy store for that matter), considering that they work via the same principle as the assays used for the initial screening at the lab?

If the sample is too pale, the specific gravity is too low, and/or the creatinine level is too low
Even urine samples with a nice yellow color to them can still register an unsatisfactory S/G and creatinine level.

you'll get a call from that cunty lady from quest telling you to come back in to retake your test.
The lab does not make that call. Thats for the employer to make that call. The lab just reports the results to the employer. How the employer will handle the results depends on the employer and the situation (eg; pre-employment, random, post-accident, etc). In pre-employment situations, some employers will grant a retest while some others will accept a negative-diluted result as "hunky dory". Still other employers will simply move on to the next candidate for hire.