Yes- they do definately stretch!
I was an 8, and had them in 8, and I wish I had got them smaller now, but the ones I got for Christmas are a 7, and they fit me better!
And the sand ones aren't too bad- I've had mine since April, and I'm yet to clean them or anything, but I've had pizza, water, coca cola, and WKD spilt on them, and they've got no stains on them- even wore them to the beach the other day!
xx