W163 W202 W203 W246 MB100D
as Deplore predicted, threatening you with big bills so you walk away, amazingto even check that it will be 250 dollars and your car still might not work with this new key
did MB confirm the first 2 things weren't a problem?AAM recognizes the key? What key # is it on now? Is the immobilizer ring functioning?
my understanding is someone with a decent scan tool can determine if the 3 things suggested above are ok within minutes (unless all are dependent on that keyring working, maybe it is). If anything doesn't work, we obviously don't know if was broken before or after they had possession of the car
update: if you bought the new key from them, I'm thinking all these 3 things should work, given you know it was working before (possible but IMO little chance it suddenly stopped working in between the time you lost the key and the time they got the vehicle)