They could've been wrong.

So I found out that my local pregnancy care place gets false negative pregnancy test kind of often. I recently went since I'm 12 days late but they said i was negative. So I'm at home, and my fiancee best friend says that his ex went there and they said she was negative but she ended up having a miscarriage. So does that mean I can't trust them or what? cause I know it can be the tests fault, but they do do the testing in a separate room and all that. Like this scares me and I don't know what to think.