well I'm guessing that if his mate bought it from another person previously then they would of updated there paperwork when they sold it or gave it to him. which you need to do anytime you despose of or sell an animal anyways. so in saying that they'd have to add who they sold it to and there details and handed that in that year when you get an renewal for your licence.
find out if your mate remembers who he bought it off and what state he got it in. then you should be able to ring the Parks to find out what this persons permit details are, or if there licenced. if it turns out that they arn't or something had happened and they lost the permit for some reason then you still won't be able to keep the snake. but if they find out what the permit details are and a phone number you may be able to get in contack with them and ask further details.
you could just say to them that your thinking of buying this snake but you'd like to find out first if these people are licenced to keep it. that way they have to check them up and you don't have to say it was your friend.
If it was me I would never take any reptile of anyone if they didn't know if they are licenced or not. too risky, plus I couldn't deal with someone coming round and taking all my animals and the fines they can dish out. you can get into deep trouble these days for looking after someone elses reptiles if you don't get there permit details off of them, found that one out few years back when a mate was looking after mine when I went on holiday. they where looking after someone elses and didn't get there details and the parks and wildlife found out sent some people round and sent my mate to court, she faced getting a $40,000 fine, and loosing all her snake 36 of them, my 4 and all the others they where looking after. luckly they got a small fine and a warning but it was so close.
if they can act on something like that imagine what the panelty for keeping an unknown licenced animal or possible wild cought.
I just say good luck anyways to you.