The paid-message-e-mail opens up like a regular e-mail, with the option to opt-out of that particular ad only after you have opened it. Personally, I'm not sure my mailbox needs more spam.
Fortunately, there is a means to disable the promotions tab, which is an option due to the outrage from users the last time it changed up its inbox. The inbox tab under settings gives you the option to choose what tabs are shown, so uncheck the promotions box and you are again spam-free.
Now, the promotions tab does serve a small purpose. It gathers up all those Groupon and Living Social emails, tucking them away to a tab you may never use, and may help to keep your real mailbox a bit less cluttered. However, you'll have to deal with the ads if you choose you use this method.