From a 3rd party?
I'm not sure if this is frowned upon for discussion but I looked in the rules all I seen was no linking their websites and no talk of 3rd party programs etc.

My main question is, do they give you the mount in game, or is it a code?

If its from a random in chat for gold, and you are refering to the blizzstore mounts then you can be very sure its some sort of fraud, and your mount will be removed very fast.

Nah not the store ones, or for gold, refering to website sales

Alot of scammers out there aswell
I would suggest you to google around and check reviews before you buy anything.

There are good website that are 3rd party to buy from..I've bought before a few

Reviews, reviews, reviews. Good luck.

Eh not worth it man to much risk involved when buying with rl money

Nah

I don't want the mount for the mount, I wan't it to sell for gold.
Figured it looks less suspicious than someone giving me like 400k in trade window or buying a random item in the AH.
I have a spare account I'd be using for the transaction either way.

Unless you are using hacks, face to face trade is usually fine providing the account youre trading with hasnt been compromised on a high level. Using your second account wont really matter but if for piece of mind, go for it. Blizzard doesnt watch everything but they do view reports.