To sell a petz, you must be the pixer or breeder of the pet you are trying to sell.
From the main menu, press the "Petz Market" button, then the "Sell" tab at the top of your screen, then choose the petz you would like to sell by pressing the "+" button in the bottom right.
First, pick a petz that you wish to sell clones of, then press the "Sell Clone" button. From here you can select the price you wish to sell it for, as well as the amount of clones you wish to sell. The player buying a clone would need to own the partz used to create the petz in order to purchase it.
Important Notes:
The cloned petz that the player receives may be generated as a shiny
You cannot currently list petz for cloning if it is wearing any items, clothing, or minimalz
The cloned petz will be the same gender as the original
When you sell a clone, you will not lose the original petz, and you will not be charged for selling clones
You can remove petz for cloning at any time by pressing the x in the top left
To create a category in your shop, you must first begin to list a petz. Go to the sell tab, press "Add Petz" in the bottom right, set a price for the petz you wish to sell, then a new popup will appear. On this popup, press the dropdown that says "Default collection", then scroll all the way to the bottom and press "Add collection". You will be given the opportunity to name it, and it will be added when your petz is listed for sale.
When listing a petz for sale, you would set the price you wish to sell for, and then press "Sell". A window will pop up with more options- this is where you'll notice on the right side it says "Who can buy: Everyone". Press the bubble that says "Everyone" and type the name of the player you wish to reserve the petz for, then press the check beside their name. Once you have the player selected, you can list it for sale as normal.
The tax actually doesn't go anywhere! Tax exists as a gold sink to prevent inflation, and to discourage cheating.
There are lots of great resources on Wikipedia if you would like to learn more about how gold sinks work in games and why tax is necessary!
Currently you can only sell back Lux partz and DYO partz. To do so, head over to the partz shop and press the "$" tab next to the coinz and gemz tabs. Select the part you'd like to sell and a purple "$" button will appear. This button allows you to sell the part you've chosen.
Seeds are a bonus given to players who make in-app purchases. You cannot obtain these any other way, and they grant you access to the Hamshop. The Hamshop contains valuable items like brushes or eggs.