Pets have always been a great item to sell in WoW. Most of them have high markups which allow for huge profit margins, and the best thing is that people are willing to pay absurd prices for some pets. Vendor pets, Hatchling, Whelps, Oozes, you name it there is probably a pet for it.
One thing I simply love doing is utilizing my alts, how? I park the at the location of the hacthling nests - which give me a chance of making an easy couple hundred gold if not more for simply logging in and checking if it's there. There are/is a total of 4 hatchling nests that can be "camped" - I will name them below and show you the possible spawn/locations of the nest below.
|Location: Un'Goro Crater|
|Location: Wetlands - Inside a cave|
|Location: Dustwallow Marsh|
|Location: Northern Barens|
If you have a lot of alts, I suggest you give this a shot - the hatchlings can fetch a pretty penny at the Auction house, and they sell rather well on my server whenever I list them.