A good tactic when possible, but Comcast requires a 3-month away period to qualify as a new customer. I think the best tactic is threaten to quit, if that doesn't work then phone back another day and try your luck again with the call center lottery.
Though you can do like I did. Call to cancel cable, and they reduce it by half bringing your total package of cable/internet to a more reasonable price. I guess they have a greater fear of showing declining subscribers than sticking to their (outrageous) price.