I really do think that the best way to overcome this is to wait untill your period is late before testing.

I know how hard the TWW is but in all honesty waiting a few extra days to have a more accurate result has got to be better than such dissapointment.

When I was TTC for Angus I had a +ve HPT so when I went to the Drs and tested -ve there. It was heartbreaking and I bawled for hours!
The Dr reassured me that the tests they use test for a higher level of HCG than the early tests used on the market and to come back in a week for a repeat test if AF still hadn't come.
They test for a higher level of HCG because many (I don't have a stat in front of me right now so I'm saying many...) fertilised eggs do not develop into pregnancies for whatever reason.
Sure enough a week later I tested BFP at the Dr's and I didn't waste any more of my money POAS at home.


This isn't directed to anyone in particular. I'm just trying to be a help and I think that maybe if you are being upset by "false positives" then maybe change the way you test.
Chances are that there was a fertilised egg that was making the test show a feint positive but then the PG hasn't continued.