I have our adopters read our care packet (chin care info, safe pet store chews) and then fill out an adoption application. Some questions on our application include things like the type of cage, shelves in the cage, what are good treats, and so on. If they have plastic shelves and show no inclination to want to change those.. they can't adopt. If they have a cage that's mouse-sized, no adopting. Assuming people stick with what they say on the form, I think the grand majority of the people we adopt out to really do care about the chins and want to do what's best for them. I tell people that we're open to them for lifetime of chinchilla support, and they can call/email anytime.. I have people that will call and ask about various things, and I think, you know, they called.... they wanted to be sure they are doing the right thing.
...and I do think the adoption form itself prevents some people, who might not have the chins' best interests at heart, from even trying to adopt. I attached our adoption form just as an example...it asks for name, address, etc. The people who have bad intentions probably don't want to let you know where they live. For every chin we adopt out, I get a variety of people who are interested in adopting the chins... but when I send them the application, I never hear from them again. I don't know exactly why, maybe they can't be bothered to fill something like that out, maybe it's below them, maybe their intentions aren't the best... whatever the case... no application, no adoption. Sorry. The people who do fill it out seem to be the people who really want the best for the chins.
We also do have a section where the person has to agree to contact us before rehoming the chin/animal. Again, no agreement, no adoption. In 9 years, we've only had four animals returned (2 degus, two chins). For three of those, the owners called us back up and asked us to take the animals back (for the fourth, we ran across their ad on a classified site)... I think, though, in the majority of instances, the majority of people really would call us before rehoming the animal, and that gives me some additional peace of mind.
I don't do anything really specific to keep in contact with the adoptive homes.. though I do have their email and their phone number (and address I suppose - all from the form) so I do have options to get ahold of them if needed. Many adoptive homes keep in contact with us completely on their own - they want to let us know how the chins are doing.
Every once in awhile, I will email some of the more recent adoptive homes (say, a few months after they've adopted) and ask how the chins are doing, if they have any pictures... and (so far) people often gush about how happy they are with their chins...
Something I started doing recently is adding new adoptive homes as friends on facebook and then suggesting they "like" our fb page... I'm actually in a seminar all day (still), but I actually spent a lot of the day messaging back and forth on facebook with an adoptive home that's coming tonight and wanted to discuss chinchilla care, health, and genetics, and how to best set up shelves in a cage. Facebook is a surprisingly good way to keep in contact with homes.
We're the same as any rescue, we want the best for the chins. If for any reason we get a bad feeling about someone we hesitate to adopt. If there is anything, ANYTHING that draws the slightest bit of attention, we address it. If for some reason I'm worried about what someone might use as treats/chews, even though they've answered that question on the adoption form, I just ask them about it. Same goes for anything - until I'm comfortable, the chins don't go home.
We do sell supplies as well... I would assume people don't buy 10 pounds of Mazuri if they plan on feeding kaytee... so that helps, because by selling the supplies, when they buy them, I know they're getting the correct supplies.
And sure, there are times I worry.. but then the people tell me how they let out the chin and how it runs around.... we just had a lady come and get a 2nd rescue from us and she was telling me how the first one wall-surfs and gets as high as the dresser, and how the chin grabs pieces of paper out of the notebook of their kid... you can tell from the people talking, especially like on the phone when you can hear them talking... you can tell they really care for their chins and think they're awesome...and for me, knowing I was able to hook them up with a pet that they're so crazy about makes it all worth it.
Sorry, thought that would be more brief!