testing after FET

When did you all start to test, my clinic said to strictly wait for the BETA but I caved in and did a test FRER for day 5 of a 6 day transfer, and it’s negative and I’m feeling so disheartened. I may have tested too early but I see so many posts on here with women who had positive tests 4-5 days post transfer. When can you trust the tests to be accurate?