Seen people sell cheap antivirus software by selling the activation key only.

The idea is that you download the software you want as trial from the official website, then activate it using the activation key.

Is that legit? Will I still enjoy full support as I would by buying the actual boxed product?

dont think so..
there's always keygen outside..
can say easy money or illegal traders.

by right you should be receiving an email of your key or its in the box.

Plenty of people openly selling activation keys here on LYN.

I don't see the moderators giving a sh!t (unlike when someone sells pirated warez, immediately kena punya), which is why I'm wondering whether it's legit or not.

selling activation keys for software is totally legit if the reseller is legit. Means they can proof that their keys are really from the company or if they are certified reseller.

Most keys sold here are fake especially on AV. There are already some cases with Kaspersky.

authorized seller will have a certifate from the company... me buying online key till now still worked... only 2month left

AV? Adult Video?
to watch porn need keys?
p/s:-seriously, I never buy keys coz some seller give fakes.

the serial key can be generate by keygen...a lot of hacker/cracker out there...
if the serial is legit,the seller should tell the customer where they got the serial key.

i have used from 1 of the seller, afaik, nothing problem on my KIS.. no blacklist etc.

AFAIK, the key should be provided in the box upon purchasing the AV. So why the need to buy the key from resellers?

It is legit as long it is genuine and has software vendor authorization...some software vendor only authorize reseller to sell activation key, some box and some both...and some software vendor onli have activation key to be distribute by reseller or distributor

If the serial key is legit then it is legally to do so I think.
Since the software activation normally require a legit key to do so, if you do not have a legit key you can't use the software anyway.