I got a false positive once, then I read the instructions and found I hadn't weeed on it long enough. It went positive for about an hour and then went neg. When I got a proper positive it never faded so I knew it wasn't right.
some tests give you evap lines, but thats usually after the 10 min waiting time. I have never had a false positive but have been pg and m/c 3 times so it can feel like a false BFP if you test then test again a few days later and you then get a BFN.
I did get a false + once, it was with an internet cheapie and all other tests after that were -. I was actually pg that month though and got + about a week later. I have had lots of evap lines, but that false one was actually pink.
I think they are rare though, especially on the more expensive pink tests. I would steer clear of first response though, for me there positives are very weak looking. You need a test with lots of dye which will give you a definate yes/no. Superdrug have nice strong positives.