Hi @lemouth, morphologically if there are differences, the confusion is between the juvenile stage (juv) of the saffron finch and the adult stage (ad) of the wild canary, which are very similar.
In adult state both species are very different, as you can see in the following drawings.
The adults are best appreciated in the following photos.
In addition to the wild canary, the subspecies known as the domestic canary is the most widespread in the world and is made up of many breeds that vary in color, shape and song; all obtained by artificial selection. Some examples are the following.
I agree that young saffrons and adult canaries (at least its yellow version) are very alike. I however thing that with experience, it becomes easy to spot the difference, doesn't it?
In any case, thanks a lot for all these pictures. They are beautiful and well illustrating the point.
Between the juvenile saffron finch and the adult wild canary, I think it is necessary to have a lot of experience observing them closely, from far away I believe it would be very difficult to detect the differences.