Anymore ecommerce is rife with popups admonishing you to 'stay in touch' with a vendor with whom you may not even ultimately do busines by plugging in your email address for a discount on your transaction.
The scenario involves going to a site. Looking around for quite a bit less than a minute and boom ... a popup with mailing list and superficial 'deal' offers appears in the way of what you're doing.
Now, while I'm sure some well meaning web developer is just accommodating the bidding of the client in these scenarios I for one simply close the browser with extreme prejudice on each occurrence so that they might know this behavior is unsatisfactory and will not be tolerated. After all, in ecommerce as elsewhere:
Caveat Emptor: let the buyer beware.
If they will walk on you during visits from the web they likely will treat you far worse over time.