An online one - follow-up emails after you've been browsing from websites with a faux matey, 'Ooh, you were thinking about this item - did you forget to buy it?' message.
Ooh, eBay do that. Somebody sends you a link (or posts something on MN) saying "Will you ever take a look at this hideous monstrosity?!" and eBay clings on for grim death, sometimes for weeks, convinced that you're desperate to buy it and that a 2.5% discount will surely seal the deal for you.
Not actually retail, but ITV stalk you in the same way if you start watching something on the Hub and then don't finish watching it. They email you asking if everything was alright as you didn't watch it to the end. Yes, because I clicked on it by accident or it rapidly turned out to be infinitely crapper than your glowing blurb promised it to be.
Like getting near-fatal food poisoning at a restaurant and them offering you vouchers by way of apology 'to use when you next visit us'.