I suspect you clicked on one of the numerous ads that will sit on top of the stream you wish to watch when if first renders, and one of these then asked for your card details.
The trick with these ads is to just wait for 15-20 seconds and then very carefully look for the small 'x' to close each...
Agreed. They vary, obviously, but are largely decent. The Ryder Cup has been streaming on my TV on a 200kbps Wiziwig stream for the last 3 hours and it's been fine throughout.
They want to display you the various markets they have on the event they are streaming. If they went full screen you might just watch and forget to bet.
Because of this, we just use the dodgy streams as we have a Mac mini connected to the TV so want full screen too.