
In my personal experience an older puppy or adult dog when rehomed is usually homed free. There will usually be quite a lot of work and adjusments that the new owner will have to make. when they buy a pup they get a clean sheet, with a rehome/rescue they are taking on baggage, and don't usually expect to pay for it. the only time any of my rehomed pups have had money change hands is where the new owner and old owner having been put in touch with each other by me and have come to an amicable agreement.
The ones I have taken in myself have usually gone tthorugh my network of dog contacts to someone who cannot afford to pay for a pup, or wouldn't buy one as always home rescues.
If I had a pup under 6 months back then I might ask for something for it, and after taking off reasonable expenses would pass any surplus on to the old owner, but this has never happened to me. They usually come back when they are less than lovable adolescents, or as full adults.
As has been said before I am grateful to find the right knowledgeable home without expecting payment.