I actually work for the Winmark in Seattle, which is the main office for the company. For the most part, the company is reputable and will pay you for your work. However, you will probably see one or two sales missing from your paycheck pretty consistently, and the company is slow and reluctant to look into and remedy the problem. You really have to be a stickler with Winmark, and the better salesman you are, the more they care about trying to make you happy.
My personal advice would be to go for it since Winmark does pay far more than any other contracting company, plus you are selling Comcast, so it really isn't that hard to get sales if you know the product info and stuff. And if you have door-to-door experience, then selling Comcast should be a walk in the park for you. Just make it clear to them from the get-go that you have heard that they don't pay their contractors 100% right and that if they try to screw you over you're done with them. This will be a lot more effective if you are actually good at what you do.