False positive on internet cheapie?

Sarah
I bought 50 of them from eBay last month and have got slightly addicted to them! 
I'm on day 10 of my cycle and my period this month was a few days early and seemed normal enough. I decided to test though on day 6 (crazy I know!) and got this faint pink line. I used the same urine to test on two more sticks and they were both negative. So definitely a false positive? All tests since have been negative too. 
I'm clutching at straws and telling myself that 49 of the tests are faulty and the only one that shows a faint line is working! Talk about clutching at straws!