I have a Vanilla myself. What I look for in a Vanilla is a couple of things. One is the headstamp. All Vanillas, even poor ones, have a bright headstamp. The second thing is coloring. Quality Vanillas are creamy bright. They have a distinct all over yellow hue to their body and markings. Many have faded heads along with the headstamp.
They can have reduced patterns or busy, and they need clear bellies.
Just for grins, I'm including pictures of my Vanilla boy so you can see what I mean.
Closeup of his head. You can clearly see the all over head blush and headstamp:
Body picture, here you can see the general all over creamy coloring he has:
A couple comparison pictures. The first is my vanilla next to a normal:

You can see how even though the normal has the faded head, the colors are night and day different.
The next picture is my Vanilla and my Fire. This picture is good at demonstrating the difference in the colors. The Vanilla is on the bottom and the Fire on Top:
Notice how the Fire leans toward cream and the Vanilla toward yellow in the coloration.
Now for my hatchling Vanilla. See the clear headstamp:
I hope this helps you a little bit in your quest.
Gale