There are a lot of pet collectors in the game, and some pets are more rare than others. For example, most engineers don't even know that you can make gold selling things to pet collectors so you often have little to no competition selling engineering pets. I've made the most gold selling Personal World Destroyer companion pets since I reached 475 engineering.Do you want more gold tips? Don't forget to share!
Goblin Engineering required
If you are a Gnomish Engineer, you have to create De-Weaponized Mechanical bunnies instead. Bunnies seem to have a higher average price, but I don't have gnomish engineering so I can't verify how well they sell. At least everyone seems to love mini fel reavers, so let's focus on those for the moment.
The materials are extremely cheap from my experience.
You can make 2-3 EEs from 2 x Volatile Air. If you have any leftover EEs, you can sell them for a lot of profit. Surprisingly many people buy them from the Auction House even when it's 400% cheaper to make them yourself/ask someone for a favor.
So how much should I ask for one?
Companion pets have crazy high price ranges, varying between 10-10000g so I can only tell you how much I've been selling these for. I usually have only one competitor, but I can still sell these for about 800-1000g each. When my nemesis takes a pause from the selling, I've been able to sell these for even 5000g each. I like it because the materials costs less than 100g for me.
To make even more profit, look for an engineer from the opposing specialization, and ask them to create some bunnies/fel reavers for you in exchange for your materials and a tip. But make sure the other engineer is not mass selling the same pets or you have too much competition.
More pets to come... Check back later!