Always very hard to say. I can only say that the Paul McGann doesn't match what I have, but people's sigs do change. Terry Nation looks like it should, so does Davidson.
I'd suggest to your friend that if they buy they might consider using Beckett authentication service. It won't be cheap or quick but they would at least know if they are real or not (unfortunately they would have to buy them first but if it turns out any are fake they could open an Ebay case I guess?)
It's always best to buy from a reputable source if possible so I'd recommend looking here first, Showmasters recommend them (You can find the post about them in the main General Chat forum somewhere), and I've bought from here before as well https://celebrityinkautographs.co.uk/index.php?route=product/category&path=25_293 (there's a separate page for new Who auto's)
Finally, Showmasters have been auctioning stuff off on their facebook page and they have a dedicated Who sale on 9/6 at 7PM (this is fastest finger first as they post an image of the 8x10 with a note in the post saying who it is, the price and how many they have, and the first to reply get it at that price. So you have to be quick)