Just because someone has a green rating for their response time doesn't mean that they'll always respond in time 100%, because it's based on historical figures. You may be right though. I'm just saying that personally, I've never seen anyone with below a yellow response rating (<30 mins on avg) have their ads listed at the front.
On a side note, if you think that the payment method you are selling with is hindering your exposure, perhaps labelling it as "other online payment" instead will help. WU, Neteller, and gift cards seems to be omitted but it doesn't seem to apply to the "other online payment" category.
That has more to do with the last online stat, as opposed to the typical response time.