First I have to say that my knowledge of grafting is.... NONE And I
suspect it will remain like that forever

This said: I have heard of it before a few times and I remember that when I
was a kid one of my neighbours had one (at least he claimed!)
orange/pomegranate... The oranges if I remember correctly were red inside
(some more orange than red), but not as red as sanguinello.

Probably the guy in the nursery was talking rubish (to be fair all the trees
I got from them were good quality), but I just want to be sure that I am not
buying the wrong tree.

PA