1)The fact it is a cpo is a very good thing.
2)Ask for a carfax and look it over carefully. Is it a local car. Did the dealer sell it to the original owner? Original location? Was it a lease or personal owner. Any consistent issues. Did it get a 1200 mile check up? Who did it? Note the in-service date as that tells you the end of the cpo
3) Did the previous owner(not leasor) buy "extended maintenance?" If so it's yours.
4) Price: You should be able to get a new one for $1000 over invoice. Go to this website bmwconfig.com/ , configure a new one like the one you're thinking of and I think you'll see your car is over-priced. Look around cars.com ( all over the country) and compare what other (particularly private sellers) '11s are selling for.