As a small ageny we gained a new client. Now we've got a problem because the old agency is the google account owner of our client. Do you see any possibility to get this account in order to not losing the history?
Hi, No you will lose the history. The corect way is to have the client set up their account (or you could do it for them) and access it via your My Client Center - see the google help videos - google.com/adwords/learningcenter/ The best you can hope for is a file with all the data in - the client should be able to get this from the existing agency. If they can't well they're probably better off without them.
You could simply try asking for the details.. I doubt it will work though. Legally it would be the other companies account.