Thanks for all the suggestions/comments/experiences. They are all most useful. Some I can't follow through, as (I think) they require a more advanced Anc sub than my friend has, and money is tight.
One question (and sorry if this is naive). In the Anc matches, I have filtered on just Paternal. Within that, when I look at each matches "Shared Matches", they seem fall in to two distinct groups that share (seemingly randomly) with others within that group, but not with the matches in the other group.
Is it a reasonable assumption that these two sub groups of the paternal matches represent my friend's paternal grandfather and paternal grandmother relations?
And further, if I work up a couple of trees for each side, they "should" (could) vector in at my friend's mysterious father?
Lastly (and more of an opinion thing)...
Why do people get tests done, appear as matches, only to not have trees and not have a user name that gives any clues how they might tie in? Not having a go in any way, just curious why.