Welcome to the site Juan.
If you get ahold of Maxum customer service they may be able to hook you up with an owners manual. But, given the age of the boat, you might not get lucky. http://www.maxumcustomercare.com/
Click on the Contact Us button.
I think you can tell a lot about a boat by the condition it is in. If it's in nice shape, especially for that age, it's a bood bet the owner maintained it well. Nevertheless, you would do well to have a marine surveyor check it out from stem to stern, including the engine and drive.