Be extremely cautious while communicating with the owner. Even if you casually agree to buy the domain via email, the communication might be used against you in court as a legally-binding contract should you change your mind. Until you’re absolutely certain that you want to make a deal, agree to buy the domain provided that all the terms are agreeable. This will leave you an escape hatch if things go south.
Check to see if you get any email accounts. Many web hosting companies don’t include email or charge extra for it. In many cases, you can only get email forwarding. Even for straightforward POP3 email, some companies only offer 1 or 2 email accounts. You should make sure you get at least 15-20 POP3 email accounts included free of charge with your domain.
By definition, a domain name is simply a human readable form of an IP address. In function it is the destination that you type into a web browser in order to visit a website, such a www.google.com. Metaphorically, it is very similar to how you would scroll to a contact in your cell phone rather than manually dialing the person by entering their full phone number; the phone number would be an IP address and the saved contact would be a domain name. Always buy a domain with a reputable domain registrar.