It isn't a matter of trust it is a matter of titers going up which happens as does age. That is why people test annually.
A one time test really isn't giving you much information.
If a doe test positive and it is a true positive then precautions can be taken.
Friends of mine asked for all 3 test, their vet said CL was useless and did not submit for it. Despite the client asking for it. The vet is a good vet BTW just has a different view of testing.
If the test had been positive they could have taken the goat back to the breeder. The goat had just been purchased and was in quarantine.
Results came back and that is when they realized the CL was not ordered. They were not happy about it but decided they would wait til spring and do the buck at the same time as the rest of the herd. 30 days passed. They put him with another buck (his pen mate/buddy) That buck was tested consecutively for years and was Negative. Severe cold snap came in goats huddled together and lo and behold as she was giving them feed and petting them my friend felt something wet. With thick long hair the lump was not visible. It had developed and burst. Immediately the buck was removed. The pus tested and blood sent out. POSITIVE.
It takes approx 3 months from exposure to be detected. The buddy buck, because of the close quarters was now infected, and right around the time they were going to do a sample he developed a lump. Just like that she lost 2 bucks. Burned everything, including the land. Turned it into a no goat area.
1 diseased animal cost her 2 bucks. They were not cheap either. Where a $7-14 test could have prevented all of it and the goat returned to the breeder. The breeder "never had a lump" but also never tested for CL.
This happens all the time. Look at all the people on here who have gone through.
Every lab says the same thing, never rely on one test and testing should be whole herd. If people don't want to fine. But I will preach buying from tested herds because I have seen way to much heartache let alone financial loss. We got lucky with our first goats because we knew nothing about the testing. There are a lot of people who know they have crap in their herd and still sell goats to trusting people and those unaware of the risk.
I know at least when I sell a goat that I, as a breeder have done all I could.