I adopted a doxie that was the sweetest thing ever and her card said she was 8 years old. She had some bladder problems which was fine, I got her a diaper and had her on medication. (She tinkled on me while I was holding her and the lady said it was from "excitement"...she had incontinence.) Well, it turns out that the doxie was really 10 years old (via my first vet visit with her). She had records from another vet office, which the name of the vet office was given to me with her adoption paperwork (So this was information that was readily available to the agency and they chose not to divulge it.) Another piece of information they didn't disclose was that she had a history of tumors. The way I found out was via a phone call with the agency when I informed them she had a current tumor that we weren't certain was cancerous or not and the lady had told me that she had one removed before.
Long story short, my doxie had to be put down a little over a month after adopting her because her tumor was cancerous and was spreading at a ridiculous rate. She was taken to a canine cancer center here in Vegas and the doctor was great, very sympathetic and really hoped there was something we could do. She went peacefully and was a lovely addition to my family for the short time she was here.
Please ask questions and do research on pets (if at all possible) before adopting. Not only from this agency (who was rather pushy about getting their money and getting the dog(s) out the door) or any agency/shelter. Rescue pets are amazing and had I known she had that history, I could have better prepared for taking her in and knowing she didn't have long.
I understand there are a lot of great positive stories from adoption agencies, and mine is definitely one of the unfortunate ones; each animal deserves a loving home and a second chance but it never hurts to do your research and ask questions to make sure it's really a good fit and that you're prepared (entirely) for your new furry companion.