If you want a chin that has the greatest chances of being healthy you might want to see if you can find a local reputable breeder. Getting a baby will give you the greatest chance of it growing up to be friendly towards you. Chins tend to do better alone so you don't have to get two.
It is not uncommon for older ones to show up on classified ads like craigslist. The biggest advantage is that you can usually get the cage setup with the chin for very cheap. Just make sure it's an all-metal cage or you really should get one. Plastic cages can be chewed and the pieces can cause bowel obstructions.
The big downside is that you won't always know what their lineage look like, as health problems can be inherited from bad breeding practice including tumors, heart problems, and seizures. You will want to make sure they have had the right diet and unlimited access to chew toys growing up, since wrong diet and lack of chewable items can cause tooth problems that can be very expensive to manage and are not always curable. It is always best to have a vet check their teeth before you buy an adult.
If they came from a good home and are used to being handled they'll be plenty friendly. But with chins it may take a couple weeks of them getting used to their surroundings before their true personality comes out. Some have a better predisposition towards people than others regardless, just like any other animal.
It's best to save up so you can take the chin to a vet if it needs it in addition to the cost of all the accessories otherwise you'll be risking the health of your pet.
Hope this helps
