However, they are only superficial.

Definitions of superficial on the Web:

being or affecting or concerned with a surface; not deep or penetrating emotionally or intellectually; "superficial similarities"; "a superficial mind"; "his thinking was superficial and fuzzy"; "superficial knowledge"; "the superficial report didn't give the true picture"; "only superficial differences"
of little substance or significance; "a few superficial editorial changes"; "only trivial objections"
skin-deep: involving a surface only; "her beauty is only skin-deep"; "superficial bruising"; "a surface wound"
wordnet.princeton.edu/perl/webwn

Superficial is a general term meaning "regarding the surface", often metaphorically. Both in the literal as in the metaphorical sense the term has often a negative connotation based on the idea that deeper parts are also important to consider.
en.wikipedia.org/wiki/Superficial

Affecting cells on the surface. Not invasive.
www.stjude.org/glossary

(external): Toward or on the surface of the body.
dir.niehs.nih.gov/dirlep/histo/terms.html

bladder tumors, also known as papillary tumors, papillomas or bladder warts, are found on the surface of the urinary epithelium.
www.healthcentral.com/encyclopedia/408/63/Bladder_Cancer.ht...

Close to the surface or shallow
www.mctsurgeons.com/glossary.htm

Towards the outside of Eg. Skull is superficial to the Brain
www.insitefitness.com.au/lessons/Anatomy/Directional Terms....

under the skin.
www.vdf.org/Varicose/glossary.php

However, they are never completely sincere.

(disapproving) saying or doing sth that you do not really mean or believe