I have bought a few licences for ess off ebay, one was a oem licence, eset said that it shouldn't be re sold and wouldn't generate a new key so the programe shows activated , but it updates and upgrades normally so is just a gui issue, though i suppose they could refuse to provide support if they wanted if i started having issues, but i could always enter free 30 day trial key
Eset have always charged over the top on their web site for their products, in particular here in the uk, and offers on the eset usa site aren't available to uk customers , unless they use a VPN